These steps are the same as for the Left. During my last build I had issues getting the X beam to line up which is why I did it this way

Mount the Right Bottom X 2020 mount to the Right Y MGN mount with 3x M3x18mm socket head screws. Do not tighten.

Insert 2x M3x30 button head screws into the Right Top X 2020 mount than slide 2 bearing assemblies onto the screws

Thread the 2x M3x30mm button head screws until the threads catch into the Right Bottom X 2020 mount

Both Left and Right top mounts should be free to move up and down with the screws threaded into the bottom mount.

Slide the Left assembly back and the Right assembly forward(See picture)

Slide in the 460mm 2020