Insert 9x M3x8 socket head screws and thread into 9x M3 T-Nuts. Align the T-Nuts so they drop into the 2020 channel.

Using 2 2020 Linear Rail jigs start at one end of the linear rail and work your way from left to right tightening the M3x8 screws until they're snug.

Than working right to left tighten the screws another 1/4 to 1/2 turn