This is a cover for the power switch on the rear of the printer. It adds a small shield around the power switch to help prevent shut offs from unintentionally touching the switch. The back of the cover has two 1.05 mm deep square holes to press on two pieces of double sided tape (I used Scotch-Mount Double Sided Mounting Tape)
While installing, I recommend putting the power cable(not connected to a power source) through the cover and connecting it to printer to help with centering the placement of the cover.