Epson EPL-5900L Reference Manual page 108

c
8. Hold the cartridge by its handle and lower it into the printer,
making sure that the pins on both sides of the cartridge fit into
the grooves inside the printer. Slide the cartridge gently into
the opening until it locks into place.
100
Replacing Consumable Products
Caution:
Never touch the developing roller under the flap; otherwise,
print quality may decline.