Just remove the phillips head screws that hold the motor on.
The motor shaft will have a three-lobe coupling on it that interfaces with the gearbox. I believe the gearbox side is metal. There is a brown plastic ring around the metal that contains locking pins. When the brown ring and metal coupling are misaligned they lock. as long as the pieces are rotating together they turn freely. I think the rings are retained by a thin metal plate.
I’m reciting this from memory as I haven’t looked in one for three months so there may be inaccuracies but I think if you play with it you will see how it works. Turning the output shaft locks the coupling. turning the coupling with the motor drives the locking ring with it to keep it from locking.