pop off that small black dashboard trim panel right by the little trangle glass... then pull back the weather stripping around the A pillar trim... then grab on it and pull it back... you may need a trim tool or screw driver to pry on where the clips are a bit to help it.... don't worry, the airbag is pretty far behind the trim.... you can actually see the canister through the crack before you remove the trim.... the very top peg of the trim near the headliner does NOT pull off... you will have to pop all the rest of the lower clips off then pull upwards towards the headliner to unclip it...
to reinstall it, take a pair of pliers and turn that upper peg/clip that "can't be removed" 90 degrees then it will slide out... install that onto the trim and then you can reinstall everything in reverse order
if you still have trouble, look in the compass/homelink mirror instructions as it requires A pillar trim removal for wiring