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

If you're reinstalling your old back cover:

Use tweezers or your fingers to peel off the old adhesive from the back cover and frame.

Use highly-concentrated isopropyl alcohol (over 90%) and a microfiber cloth to remove any remaining adhesive residue.

Follow this guide to apply new custom-cut adhesive.

If you're installing a new back cover, peel off the liners and press firmly around the perimeter to secure the back cover to the frame.