Peel off the large blue film liner and remove it from the adhesive strips completely.

Take care not to accidentally touch the adhesive strips after this step. The adhesive is good for one use. If it sticks to your finger or another surface accidentally, it must be discarded and replaced.

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.