During reassembly:

If you're reusing your back glass, use tweezers to remove big chunks of adhesive from the perimeter of the back glass.

Repeat for any adhesive on the frame.

Use isopropyl alcohol (>90%) and a lint-free cloth to remove any remaining adhesive residue.

Follow this guide to replace the back glass adhesive with custom cut strips.

If you don't have custom cut adhesive strips, use double-sided tape, like Tesa Tape, to secure the back glass to the frame.