It depends what the power source is. HINT: If it runs off the cigarette lighter then you need to plug it into THAT - NOT the power line that runs into the cigarette lighter.
If you mean to wire the power source discretely from a power line underneath the dash, then you will probably need an auto-electric place to find a suitable wire, then to connect either a USB or a cigarette lighter connection under there.
But if you intend to use an existing USB or cigarette lighter outlet, then you should be able to snake the line around yourself, tucking it under the interior trim. Depends on your aesthetic standards, I guess.
I did mine myself, it runs from the USB inside the armrest, where I drilled a hole to let it escape to the side under the passenger seat, then under the trim by the door, under the side trim under the dash, then under the trim around the window, to the dash-cam. It is invisible except for where it emerges from the interior trim at the top of the windshield, with a couple of inches of cable there. Under the trim I actually jammed my used chewing gum in there to hold it in place. My rear view mirror blocks that view for me, but not the passenger.