Oki Microline 520 Service Handbook page 187

Reset Menu to Factory Defaults
CAUTION:
Once the menu has been reset, all customized menu settings will be lost.
Always print the menu before resetting the printer to factory defaults.
To reset the menu to factory default settings:
1. Before resetting the Menu, Okidata STRONGLY RECOMMENDS printing the
Menu.
Printing the Menu provides a reference of customized settings.
When the Menu is reset, all customized settings are LOST.
2. Power off the printer.
3. Press and hold SEL and LF while powering ON the printer.
Microline 520/521 Service Handbook
P/N 59257803
3 - 75 Maintenance