Epson EPL-N7000 - Manual (Page 241)

230 Installing Options
Note:
After removing the gear cover, keep the cover and the screw in a safe
place.
4. Install the Duplex Unit onto the printer.
Make sure that the two pins at the bottom of the unit are
hooked at the lower edge of the opening at the back of the
printer, as shown below.
c
Caution:
Hold the upper part of the Duplex Unit with one hand until
it is fastened to the printer in the next step. Otherwise, the
unit may fall off and be damaged.