First operate the switch in both directions and listen carefully to confirm there is o sign of movement at all. Also use a volt meter at the motor terminals if possible. If there is voltage when switch is operated, but motor doesn't turn, then motor maybe faulty. If no voltage, then wiring may be the cause.
My back rest didn't work, and the problem was traced down to a misplaced "socket pin" *inside* the wiring connector going to the switch on the door.