Sounds like a transmission issue.
I missed your last post. Go gentle on it. The bent screwdriver trick may help but I suspect it was another issue. Usually when you. Need the screwdriver it is because the transmission stays in a particular gear regardless of shifter position, and will also shift into he other three gears as well lacking up the transmission. Tractor will only move with shifter in the gear it is stuck in or in the neutral position. Rough handling will often result in bending the shifter forks leading to the shifting peg slipping off the forks. Best videos on YouTube by Zippo Varden.
If i were you and are not going to be using the neutral safety interlock switch I would remove it all together as it tends to bind up the gear shifter. You will be surprised about how easy it is
to shift without the switch.