Guide the power cable along the headliner, down the passenger's A-pillar to the passenger footwell. While it sounds complicated, it is pretty straightforward; all you need to do is use the included prying tool to pry the headliner so there's a gap just enough for the cable.
You also don't want to push the cable under the rubber seal because it will create a little gap that might prevent the door from sealing properly - you will get wind noise, or worse, water can seep into the car. Take your time to guide the cable under the trim, and use the pry tool to tuck the cable underneath the panel covers carefully.
Suppose you haven't done so, download and install the Thinkware Cloud app on your smartphone. Once your Thinkware Q800PRO is powered on, press the WiFi button on the front unit to switch it to WiFi mode and then connect to the dash cam using the app to check the angle of the front and rear cameras.