How do I replace the on off switch on a Miele w460 washing machine?

The machine in question would turn itself off during the wash cycle and back on again later, it may do this a number of times during the wash. It would also activate the pre-wash alarm even if the pre-wash hadn't been used. At times the machine wouldn't turn on at all even if it had completed a full wash the day before. I looked at the on off switch and checked it and the yellow plastic part of the switch looked like it was sticking, it has since fallen off and now there is no power to the machine as the button won't stay in. I need a full breakdown of how to replace it, idiots guide please as I have never tried this before and any unusual tools I may need to do he job. Many thanks