Once the battery is loose, remove it from the phone.

Do not reuse the battery after it has been removed. The stress of removal can cause hidden damage to the battery cell, creating a potential safety hazard. Replace it with a new battery.

To install a new battery:

Remove any remaining adhesive from the phone, and clean the entire area under the battery with isopropyl alcohol.

Apply a few new strips of pre-cut adhesive or Tesa tape.

If you are attaching the battery with a custom-cut adhesive, follow this guide.

Press the new battery firmly into place for 5-10 seconds.