During reassembly:

Check for any thermal paste on the frame (to the left of the front facing camera) and the corresponding spot on the back of the front sensor assembly.

Use the flat end of a spudger to scrape up any large chunks of paste.

Apply a few drops of isopropyl alcohol to a lint‑free cloth (or coffee filter) to clean up the area.

Allow the isopropyl alcohol to dry completely before continuing.

Apply a very small amount of viscous thermal paste where the old paste was on the frame.