Epson EQUITY 3865X/20 PLUS - Manual (Page 106)

Notice the icons under the screw:
locked unlocked
screw
5. The cover is also secured by two latches on the back of the
cover near the comers. Press both latches inward and then
lift up the cover from the back panel. You might meet some
resistance from the grounding tabs along the inside of the
cover.
latches
6. Pull the cover away from the front of the computer to
completely remove it. Then set it aside.
Accessing Internal Components 5-3