Remove the Lightning connector assembly.

Before installing or replacing the Lightning connector assembly:

Use a plastic tool to scour any bits of adhesive residue from the rear case. You can use some high concentration isopropyl alcohol to help clean the surface.

Before removing the adhesive backing, make sure the Lightning connector assembly is correctly positioned by aligning the hole in the flex cable with the screw post. If the cable is misaligned, you won't be able to reconnect it to the logic board.