Epson EPL-N7000 Reference Manual page 244

If your printer already has the optional 4-Bin Mailbox installed,
remove the 4-Bin Mailbox first, install the Hard Disk Unit, and then
reinstall the 4-Bin Mailbox.
1. Turn the printer off and unplug the power cord.
2. Remove all interface cables from the interface connectors.
3. Slide the lock lever to the right, and then open the front cover.
Installing Options
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