Remove the rear glass.

If the rear glass is still stuck to the frame, slide an opening pick around the entire perimeter until the rear glass separates completely.

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.

During reassembly, secure the rear glass with pre-cut adhesive or double-sided tape after cleaning the relevant areas with high-concentration isopropyl alcohol (>90%) and a lint-free cloth.

After installing the rear glass, apply strong, steady pressure to your phone for several minutes to help the adhesive form a good bond—a stack of heavy books works well.