print with 100% fill with the u-shaped slot up.
Add dial gauge, M6 nut and M6 screw. Clip to M3 long bolts straddling the Y axis bar towards the front. Top edge of thing should be touching the bottom face of the upper ply head board.
DO NOT HOME WITH THIS THING ATTACHED. BAD THINGS WILL HAPPEN.
Level procedure. Set dial to zero close to home, transit in each corner and adjust the bed screws.