Set both buttons to off (RED). Now reset the sequencer and turn on button 1 and 2 (set to GREEN).
Button 1 controls the data fed to the displays.
OFF = Clear all displays ON = Programmed message
Button 2 controls the clock.
To change the message, dump the core or reset the EEPROM and rewrite the suitable data for the 16-Segment Displays. If the new message contains lesser or more letters/numbers to show, make suitable changes to the Sequencer and change the number of displays used.