If is older it will have a code buttons inside of the unit you may have to disassemble a little of it.
Then it will be able to slide the numbers up and down like 0 thru 9 and you set it to what you want,you will also need to open your remote opener and set it to the same exact #'s you set on the unit.
If you can't figure it out good solutin is put something in the area where it goes up and down like a bolt in the holes in the rollers,or a C-clamp tightly on the slides or just unplug it,till you get it figurd out is better than getting robbed blind'