Found some info for you,
a. Switch off the Machine and then switch on the machine while holding down the ‘menu’ button until all the lights are flashing on/off. Now you are in ‘maintenance’ mode.
b. Press 80 and press the ‘mono start’ button several times until you see ‘purge: xxxx’.
c. Press ‘2783’ in order to reset the purge counter. You will see ‘purge:0000’.
d. Press the ‘stop’ button.
e. Press ‘99’ to exit the maintenance mode.