Hi I have a 1999 ford explorer and the drivers side seat belt won't plug in is this something I can fix myself?

The fuses for the seat are shared with other features on the car such as power antenna. Has any other power feature gone off as well?
Check the runners the seat slides in. There might be something trapped in there blocking the running action.
There are two fuse boxes. One under the hood in the rear drivers side corner, under a black plastic cover. The other is inside the car, inside the end panel of the dash. (With the door open).
Check fuses 1 and 18 as they cover the power seat functions.
https://autobonches.com/amp/fuse-box/2003-ford-explorer-fuse-box-diagram/

possibly there is something stuck in the belt not letting it retract

disconnect the battery and then find the sensor wiring connector under the front seats ,pull teh plug in and out a couple of times ,if no joy then disconnect battery again and plug and un plug the other end of the cable onto the pyrotechnic device at the bottom of the seat belt anchor

Maybe you problem is with the switch, or check if power seat circuit has the regular fuse or rather one of those thermal ones.
Passenger compartment fuse panel
The fuse panel is located on the left hand side of the instrument panel facing the drivers side door.

Position 18 25A - Drivers Unlock Relay, All Unlock Relay, All Lock Relay, Power Seats

yes you can. I suggest you go to the scrapyard and purchase one there. they are easy to replace and inexpensive.

It is a very plain code it has something to do withthe drivers side seat belt buckle. Either out of range short to power or ground etc. Need a more specfic code to pnpoint exact problem but I can tell ya it is in your drivers seat belt connection somewhere

remove seat - 4 bolts mounting to floor - unplug and remove seat - look for missing bolt, probly on floor under seat or in seat, reassemble seat back, install and plug in seat

remove trim - coulpe screws and look behind trim, most likely belt twisted

so after completely tearing the seat apart I found 2 wires going up to the seat belt mechanism from under the seat, these wires got caught in the seat mechanism underneath and were shredded. There must be a small solenoid inside the seat belt mechanism because I could hear it click after I repaired the wires(this circuit is live even with the ignition off) Im not sure how it all works but this solved my problem.