Using 3x M3x18mm socket head screws mount the Left Bottom X 2020 mount to the Left Y MGN mount. Do not tighten. Make sure you pay attention to the mounts. There will be a L for Left and R for right. The picture shows I used button head screws. I noticed I used the wrong ones after the picture was taken

Using a spare M3 screw slide on a F623ZZ bearing+M3 washer+F623ZZ bearing and insert it into the bearing tool. Once the bearings snap into the tool you can remove the M3 screw

You will need 2 bearing assemblies per side so it would be wise to print 2 bearing tools.