Epson EPL-N3000 Reference Manual page 207

When you install two optional paper cassette units, put one unit
upon the other unit in order, then put the printer on top of them.
3. Pull out the MP tray and lower paper cassette from the printer,
and then pull out the optional lower paper cassette from the
unit. Then, secure the printer to the unit with the four fittings
that are provided. Install two of the four fittings on both sides
of the inside of the printer.
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Installing Options