Remove the back cover.

Before you install a replacement back cover, be sure to remove all adhesive residue from the phone frame. Use an opening tool to scrape and high concentration isopropyl alcohol to clean the surface.

If you are re-using the back cover, be sure to clean off any adhesive, and apply new back cover adhesive.

If you are installing a replacement back cover, be sure to compare it with the original part. Transfer any remaining parts (such as the flash diffuser) over to your replacement part.

Follow this guide to correctly apply new back cover adhesive.