If you successfully removed the entire ambient light sensor, as shown in the first photo, continue to the next step below.

If the white diffuser strip detached and remains embedded in the display, as shown in the second photo, you will need to carefully lever it out along the top edge using a thin blade or pry tool. Re-applying heat first may make this task a bit easier.

During reassembly, install the diffuser into the display first, making sure it faces the right direction (the front-facing side is shown in the first image, and the rear-facing side is shown in the third).

Then, set the ambient light sensor on top of the diffuser. You will need to hold the sensor in position while installing the screws securing the earpiece/sensor assembly. Once the screws are tightened, the sensor will stay in place and work normally.