If you're installing a new rear glass panel, you'll also need to transfer the fingerprint sensor to your new rear glass panel as follows:

Reheat an iOpener and apply it to the fingerprint sensor mounted to the rear glass.

Push the fingerprint sensor off of its adhesive from the outside of the glass.

If the sensor is stubborn, gently slide an opening pick under the plastic backing to loosen the adhesive before pushing.

This will make the adhesive less likely to be reusable, so try pushing with your finger first.