Lift and remove the back cover.

Before installing fresh adhesive and reassembling, remove any remaining adhesive from the phone, and clean the glued areas with isopropyl alcohol and a lint-free cloth.

During reassembly, this is a good point to power on your phone and test all functions before sealing it up. Be sure to power your phone back down completely before you continue working.

Secure the new back cover with pre-cut adhesive or double-sided adhesive tape. After installing the rear glass, apply pressure for several minutes to help the adhesive form a good bond, such as by placing it under a stack of heavy books.