I have seen lots of machines with a missing/broken button
They are very easy to replace
Get the front panel off and take of the whole pcb 5 llittle screws then you can get out the push button bank.
There is a rod at the back with a very tiny almost you would miss it circlip in the middle, get that off an rod slides out, add the new button in and slide it back re- insert the clip and put all back together
Here are some photos to help