The third at a right angle is how you remove the airbag. You just slide in a torx or whatever screwdriver which pushes a lever and releases the airbag. Have to do both sides.
It's possible there are only two screws holding on the trim piece. I could have a faulty memory on that bit.
Be very careful when you remove the trim bits. I removed mine with the airbag in place successfully.
For zero chance of breaking the under mount points you could remove the airbag first using the above method. If you unplug the airbag with the battery connected you'll get an airbag light that will need to be reset with a scan tool. However you could probably just pull the airbag away from the wheel leaving it connected.
I would just gently do it with the airbag in place.
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