Now you can remove the sprocket assembly from the motor, do not loose the O-ring. Also this is opportunity to grease the bearing with good waterproof grease. Picture shows the sprocket off. BUT if you look closely, there is an Allen wrench going through the very center of the unit.
This connects the motor output shaft to the drive sprocket. In many cases this will be enough to resolve the issue, I assume, lining up the hole and assembly I will describe a bit later as there is one not of importance.