During reassembly:

Check the condition of the logic board thermal pad—it will either be on the bottom of the logic board or on the frame.

If the pad is undamaged, skip the rest of this step.

If the pad is damaged, use the flat end of a spudger to scrape it up and remove it.

Use isopropyl alcohol (greater than 90%) and a microfiber cloth to remove all thermal pad residue from the frame and bottom of the logic board.

Apply a new thermal pad to its spot on the frame.