Place the battery face down on a flat surface.

Starting at the pointed end of the adhesive strips, peel off the large blue film covering the strips.

The blue film sometimes has a defect that prevents it from peeling off, and the strips have to be discarded and replaced.

If this happens to you and you got your strips from iFixit, contact us here and we'll send you a replacement on the double.

In the meantime, you can temporarily reassemble your iPhone with a bit of double-sided tape to hold the battery.