How do you adjust the bobbin tension?

Question edited for clarity.
Please don't type in all CAPS, it is considered SHOUTING and is harder to read.

Sewing machine tension is a delicate tug of war between the bottom Bobbin tension and the Upper tension to put the loop between the 2 layers of fabric. You set the Bobbin tension first and the the top tension depends on the fabric and the thread used.

Your Bobbin tension is very very loose to be not tensioning at all or the top tension is too loose.

Adjusting The Tension - Janome Memory Craft 6500 ...

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Janome Memory Craft 6500 Professional Manual Online: balancing thread tension, Adjusting The Tension. Correct Tension: The Ideal Straight Stitch Has Threads ...

Best video on tension

There is no really correct or wrong answer here. It's trial and error, and experience with your machine. The reason? WAY too many fabrics and variations on threads. The wear in the tensioners and even the needle all make a difference. When in doubt, start with everything set in the middle of the range and test a few runs.

Usually, if there are loose threads under the fabric, it is the top thread that is too loose. Check your sewing sample closely--you can even test with two different color threads to help distinguish which thread is which. Loose top thread will generally be pulled DOWN and show under the fabric. Loose bobbin thread will be pulled UP and show on the top of the fabric. The ideal tension is when both threads MEET in the middle of the fabric.

First, remove the thread from the machine. Install a brand new needle. Always Raise the Presser Foot and thread the upper thread, making certain the thread path is correct.

Check that the bobbin thread is threaded correctly and turning the proper direction in the bobbin case.

Set the upper tension to the midway point and sew a retest. A tweaking of upper tension may be necessary to get it where it should be. Generally, upper tension should make the majority of adjustments needed for tension correction. Bobbin tension is one of the last tension adjustments to make as it is very sensitive and can go awry very quickly.

If, in fact, the bobbin tension is off, the tension skrew on the bobbin case is where the adjustment is made. Before making any bobbin tension adjustments, mark where the skrew slot is located on the bobbin case with a permanent marker. This will allow you to reverse your changes if necessary. Be CAREFUL as TINY changes make HUGE differences in tension. Make only 1/8th turn adjustment, then retest before making another adjustment.

Remember that tension testing and readjustment are a necessity when sewing. The same tension that will work with light weight thread and fine fabric will most likely not work when using heavy thread on drapery fabric. Get comfortable with making tension adjustments to get the ideal tension for each project.

Understanding Thread Tension Threads

Oh You Crafty Gal Sewing Lesson 10 How to Fix Tension on Your Sewing...

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=14&ved=0ahUKEwilg-3t2vHMAhVJDlIKHXnsBWYQFgheMA0&url=http%3A%2F%2Fwww.ca.uky.edu%2FHES%2Ffcs%2FFACTSHTS%2FCT-MMB-213.pdf&usg=AFQjCNE4QlGk1Fvt8K2UGCRCfzMpGS-A2Q&cad=rja

How to Adjust the Tension on Sewing Machine

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Make sure you raise the presser foot BEFORE threading the upper thread so it will seat properly in the tension disk.

The factory standard tension setting is the halfway point between the low & high numbers. Be sure you are using needle & thread that are compatible with each other and the fabric you are sewing.
All About Needles

Test your stitch on the fabric you are sewing. If the upper thread is showing on the bottom of the fabric, the upper tension is too loose. If the bobbin thread is showing on the top of the fabric, the upper tension is too tight.

Ideal tension is when both upper and bobbin threads meet in the middle of the fabric. The tension will need adjusting anytime you change fabric weight, needle size, and thread weight.

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Try loosening the tension for that bobbin

Remove all the thread from your machine. RAISE the presser foot so the thread will seat properly in the tension disk. Rethread from the beginning. Confirm with the owner's manual that you are threading correctly and not missing any steps along the way.

Set the upper tension to the halfway point between the high & low number--this is the factory standard setting.

Make sure the thread & needle are compatible with each other and the fabric you are sewing.
All About Needles

Make sure the bobbin is loaded in the bobbincase correctly and the thread is pulled through properly.

Test. If the upper thread is showing on the bottom of the fabric, the upper tension is too loose. If the upper thread is pulling the bobbin thread to the top of the fabric, the upper tension is too tight.

If you must adjust the bobbin tension, mark the bobbincase where the screw slot meets so you can undo any adjustments you make. When making adjustments to the bobbin tension, make 1/8th turn at a time as a small change will make a big impact on the tension.

Ideal tension is when both upper and bobbin threads meet in the middle of the fabric. If you change fabric, needle size, or thread weights, you should recheck the tension and adjust as needed.

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Be very careful adjusting the tension on the bobbin case. Generally, most tension issues are regulated using the upper tension adjustment unless the bobbin case is broken or someone has attempted to adjust it incorrectly. In any event, adjustments to the bobbin case should be made ONLY 1/8 of a turn at a time--then do a test stitch. Before making any changes, mark with a permanent marker where the screwdriver slot meets the bobbin case in the event you have to return it to the original position.

If the top thread is looping or knotting under the fabric (bird nesting), the upper thread is too loose or it is threaded incorrectly.

If the top thread is pulling the bobbin thread to the top of the fabric, the upper tension is too tight.

Tension is ideal when both threads meeting in the middle of the fabric.

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According to the manual, you should not need to adjust the bobbin tension (and I located other sites which stated the bobbin tension cannot be adjusted on this machine). Apparently, all the tension adjustment is accomplished through the upper thread::
"EN Thread Tension Upper thread tension Basic thread tension setting: "4". (1) To increase the tension, turn the dial to the next number up. To reduce the tension, turn the dial to the next number down. A. Normal thread tension for straight stitch sewing. B. Thread tension too loose for straight stitch sewing. Turn dial to higher number. C. Thread tension too tight for straight stitch sewing. Turn dial to lower number. D. Normal thread tension for zig zag and decorative sewing. Correct thread tension is when a small amount of the upper thread appears on the bottom side of fabric. Lower thread tension The bobbin tension has been set correctly at the factory, so you do not need to adjust it. Please note: - Proper tension setting is important for strong seams. - There is no single tension setting appropriate for all stitch functions, thread or fabric. - A balanced tension (identical stitches both top and bottom) is usually only desirable for straight stitch construction sewing. - 90% of all sewing will be between "3" and "5". - For zig zag and decorative sewing stitch functions, thread tension should generally be less than for straight stitch sewing. - For all decorative sewing you will always obtain a nicer stitch and less fabric puckering when the upper thread appears on the bottom side of your fabric. 1 A B C 22 D"

Doing further research, I found this statement on a machine review site:
"After reading reviews online from where I've bought my drop-in bobbin machines, I think many of the negative reviews are due to the bobbin thread coming up without laying across the bobbin. It can cause the stitches to look very sloppy and no amount of tension adjusting can fix the stitches."

There are several machine review sites wherein 4423 owners stated their disappointment in the 4423's performance. Some said the machine failed almost immediately and others said the machines developed problems when sewing heavy fabric.

the bobbin tension is set by that small spring plate that you pull the thread under after you put the bobbin back in the carrier / holder
a very small turn of that screw makes a big difference ob the tension unlike the needle thread tension
mostly the problem ( you never bothered to mention the symptom ) is bird nesting under the fabric which is the needle thread tension not tight enough

When you thread your bobbin in the bobbin case, hold it only by the thread. If the bobbin and bobbin case fall, the tension is too loose. If this is the case, turn the bobbin tension screw 1/4 turn until the bobbin and bobbin case do not fall when only holding by the thread. The top tension should be set between 4 and 5. The best way to see which one needs to be adjusted is to do a zigzag. If the thread is pulling more on top and your top tension is set between 4 and 5, the bobbin tension is too loose. If your top tension is set between 4 and 5 and it's pulling on the bottom, the bottom is too tight.