Put a Philips screwdriver through the hole and engage the screw head. You can see it through the end panel. Push moderately hard to set the point into the wood, and tighten it down. The screw has to thread through the retaining plate and into the wood. If you don't press hard enough, you will feel resistance as it enters the plate, but the motor will lift up. Once the point engages with the wood, it will tighten down.
Go until the screw starts to tighten, then back off half a turn.
Now, make sure that the motor is all still aligned. You can move it by swiveling around the first screw. Use the cashbox base as an indicator.