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, in order to soften the adhesive securing it to the rear glass.

Push gently but firmly against the fingerprint sensor from the outward-facing side of the glass panel, until the adhesive securing it separates.

If you have trouble pushing the fingerprint sensor out, apply more heat, and/or carefully slide a pick along the edge of the sensor to cut some of the adhesive.