You need to do the following:
- Find the cables that go to the speaker. These are directly accessible.
- Find a ground connection pin. This should be marked on the PCB somewhere.
- Find the opener pin. This is the the hardest part. For physical buttons, find the wire on the PCB that goes from the button to the micro controller. For Touch buttons you will need to measure each pin coming from the touch panel going to the micro controller while pushing the door opening button. Measure each pin while pushing the button and see which pin changes with your pushes.