Siemens extraklasse diswasher - on/off button?

I have a siemens dishwasher which is brilliant. This morning the on/off button has broken. It has fallen inside the door. It still worked to turn the machine on and off if I pushed it in the right direction but now it has fallen further in and I can't get it to work.
I've found the spare part button online but I need to know how to fit it?
Is it easy to get to, to enable me to put the new button on.
Thanks in advance.....