’02 shifter issues

Trying to get my sons sportsman 500 up and running. Shifter froze in low and would not move, my son has managed to get it back to neutral(lights on) but will not go into any gear but low. Drove the quad in all gears last week, no problem. Son says this has happened before and force worked then. Seems to be the shifter itself but i’ve been wrong before. any ideas?