here is a good video for reassembling the flex cable. It is not simply "everything in reverse". https://www.youtube.com/watch?v=-NeW5Lzt...

I replaced the cable with the power switch AND put everything in a replacement housing. My power button clicks and works fine, but it a bit loose, so as if there is about 0.5mm space between the button and the switch. In the original state from the factory, the button sits tight. Anyone an idea?

you can use thin pliers and a screw driver to "bolt out" the old one with force. then use the Pentalobe screwdriver to widen the pin hole in the new housing a little bit, then drive it in with not too much force (in order not to break it). I found these instructions on the internet, and it worked for me - many replacement housing seem to lack that pin.