Thread in the M3x30 with bearings on it into the top plate to prevent the bearing from falling out.

Position the bottom plate so 4x M5x8 button head screws so the T-nuts will drop into the channel. Do not tighten completely.

Using a M3x6 socket head screw attach the bottom plate to the stepper but do not tighten.

Insert 2 bearing sandwiches (bearing+washer+bearing) with the bearing tool into the assembly and thread in 2x M3x30 socket head screws

Insert 1x 19mm standoff spacer and thread in a m3x30mm socket head screw. Do not tighten

Tighten the 4x stepper screws.

Tighten the bearing screws. 2x on top and 1x on the bottom. Tighten the standoff spacer screw

Tighten the 4x M5x8mm button head screws on the bottom plate