Turn the MFP off and then on.
When the memory count appears on the control-panel display, press the right-hand side of the START button until all three LEDs are lit. Release the START button.
Press 5 one time. INITIALIZE DISK appears on the control-panel display.
Press 6 one time. A series of asterisks appears on the control-panel display. Wait for the MFP to complete its initialization sequence.