Can it be, that only gear 1 and 2 works or is it really stuck in gear 1?
If reverse gear works and it switches to 2 and if you can move the switcher from P to 1 and back with feeling the wires move, there is a deeper problem with your tranny and you should rebuild it with new sun wheels or to replace the entire transmission.
If both are no, then the gear switch wire is blocked or broken. Try to put one or 2 drops of oil on the engine side and switch the selector a few times from P to 1 and back. It it works -> ok, otherwise you have to replace the wire