Epson 20 - Manual (Page 147)

Once you confirm the DEVICE LIST, you can test only those items.
If you decide later that you need to add a device, you must return to
the OPERATION MENU and re-select System diagnostics.
Modifying the DEVICE LIST
If an installed device is missing from the DEVICE LIST, it is
important that you add it to the list and test it carefully. In response
to this prompt:
Is the DEVICE LIST correct (Y/N)?
press N followed by Enter. You see a new menu:
Modify DEVICE LIST
l - Add devices
2 - Delete devices
0 - Exit
Enter selection number:
Performing System Diagnostics C-3