Use a JIS 000 driver or an official iFixit PH 000 driver to remove the following screws securing the rear panel:

One 2.5 mm-long screw on the top edge of the device

Two 2.5 mm-long screws on the bottom edge of the device

To prevent these tight screws from stripping, apply firm downward force, work slowly and try another JIS 000 or PH 000 driver if the screws won't come out.