During reassembly, follow this step to replace the plastic shim that runs across the bottom of the midframe and loudspeaker. If you don't have a replacement, press the old one back into place.

Remove the larger rectangular liner from the shim.

Place the shim so the smaller piece of foam lines up with the bottom of the USB-C port cover.

Use the flat end of a spudger to firmly press down along the whole shim to secure it.

Remove the remaining liner.