The first thing I would try is unplug the shift motor and put power to the 2 terminals (1 power 1 ground) and make sure it's working
The shift motor is on the front of the motor, towards the bottom. you can check it without taking it off, the connector is on the (mid/front) right side of the atv. if the motor checks fine then it could be broken wire, bad connection, ecm. ? the 30a motor fuse is good