Reinstall the four silver Phillips screws securing the trackpad to its steel brackets.

Loosen all four silver screws about 1/16th of a turn.

Flip the upper case over and adjust the position of the trackpad until the gap between the trackpad and the upper case is evenly spaced around the perimeter of the trackpad.

Tighten the four silver screws to hold the trackpad in place.

Repeat this process until the trackpad is perfectly positioned in its void on the upper case.