During reassembly:

Use tweezers or your fingers to remove the old adhesive from the top of the earpiece speaker and back of the antenna.

If your replacement part doesn't include new adhesive, use a 4 mm x 16 mm strip of thin, double-sided tape to secure the antenna to the earpiece speaker.

Slide the new antenna underneath the front camera cables and make sure its cable routes in the channel above the logic board.

Connect the antenna press connector, and press the antenna onto the earpiece speaker to adhere it.