You must have its remote control to make it to factory reset. If you wish to buy its original remote control, contact the authorized service centre, or authorized dealer to your device brand. They can either give you a genuine remote control to your device, or can direct you, from where can you purchase a suitable one.
If you have the remote control, just enter its service mode; surf through and select the 'Factory Reset' option, and press OK.
If you wish to get some details; check the site linked here.
Pull up older posts. Surf the site with patience.
http://electronicshelponline.blogspot.com/
Service mode entry, adjust and exit procedure to many popular brand TVs are given. Never forget to exit the service mode, after all adjustments have been done.
Sorry to say that nothing more can be done without its remote control, other than contact the authorized service center for help.