If you are installing a new part, your new part may have two tabs with holes in it used for manufacturing purposes. These tabs can be cut off with scissors.

There is a small, square plastic and metal holder for the proximity sensor. This holder is essential for the proximity sensor to function correctly.

If replacing the proximity sensor or camera make sure that the holder remains adhered to the back of the display. If it comes off with the old proximity sensor, remove it from the old sensor and use a tiny bit of adhesive to re-attach it to the back of the display.