Disclaimer; I'm publishing this info, because it seems to work for me on the oven I bought, I make no warranties that any of this is true, reliable, consistent or will work for you, and most expressly; you try any of this at your own risk. If you hurt someone or damage your home as a result - it's your own fault for playing with things you shouldn't be playing with. These menus are meant for use by Miele authorized service personnel, if you aren't one of those you should call one and leave well alone.
There are two menus; The Service Menu and the Programming Menu;
These menus are accessed by certain key combinations on the front panel;
Then press the Clear button 3 times (each time you should hear a beep). On the third press hold the button (do not release it). After a couple of seconds the display should show the Service Menu.
If it didn't quite work, you probably left too much time between releasing on/off & clear before pressing clear 3 times. Alternatively you may have miss counted the number of presses of clear.
Copyright (c) 2010 A. Saulsbury.