Turn off the printer and move the extruder to the centre of the X axis.

Relax the tension of the X axis belt. Refer to the manual for your extruder if you are unsure how to do this. (Note! this was shown in step 06. Z axis motion.)

Loosen the screws which secure the trapezoidal nuts. This is to ensure that the Trapezoidal nuts 'self-centre' on the lead screws.

Make sure the trapezoidal nuts are able to move freely.

Alternating between all 4 screws, incrementally tighten each screw to secure the trapezoidal nuts (alternate between both sides during this process). Don't apply any lateral force to the trapezoidal nuts.