Take both wheels off
Using a 5mm hex wrench loosen the set screws on the rotor mount and drive gear mount. Some versions had set screws with nuts on them; these use a 10mm wrench and a 4 or 5mm hex key.
There is a square axle key under each axle component that engages it to a slot in the axle. The idea is to push those out and you can then easily slide the axle out of the disc and drive mount.
The axle slides out of the axle carrier towards the left/non drive side (when upside down this is the right side). This can be done without having had to remove the drive chain and brake caliper, but it is easier if you remove those two items.
With the axle removed you can pull out or push out the bearings on each end of the axle carrier.
Push the axle all the way until the drive flange butts up against he left outboard bearing.
Install wheels with proper non drive wheel spacer in place before adjusting position of drive gear and rotor.
Line up drive gear so drive chain is straight before locking down the set screw.
Line up rotor mount so that the rotor is centered in the caliper. Adjust caliper for proper brake function.