How to change microswitches (left/right "mouse button") on Logitech G700?

Okay I got it! The mouse is working just fine.

The 14 points on #3 are "Rectangular Connectors/Headers/Pins".

I had to unsolder them one by one. After that I was able to lift the board.

Here is how it looks like underneath the first board:

After that you just have to unsolder the three points from the microswitch you want to change. Put it back together and you're good.