Try this as it works on other Miele Washing Machines, hopefully yours too!
Press and hold the Start/Stop button while switching the unit on with the On/Off switch.
As soon as the Start/Stop illumination ring lights constantly, after approx. 5 sec., release the Start/Stop button.
Immediately press and hold the Start/Stop button until the Demo-Mode is deactivated, approx. 4 seconds.