Iwatsu ENTERPROSE-CS Owner's Manual page 205

Group Night Mode key without the group parameter maintains the legacy key
operation regardless of the type of telephone. The key can only toggle between
Day (Day-1) and Night
 Press the Group Mode key. The current ringing mode is displayed in
reverse video
 Press the Day-1, Day-2, Day-3, or Night key to change the ringing
mode. The new selection will display in reverse video and Mode
Change Successful will appear on the second line of the display
 Press Exit to return to the main display. The new ringing mode
selection will appear on the display
ATTENDANT POSITION USER GUIDE - 187