Putting your key in the switch was a little difficult for me. I did it at night and since the switch is on the right side of the side wall of the glove box, the light from the glove box doesn't shine on it. I spent a couple of minutes 'feeling' my way around the switch.
After you turn the airbag off, a light appears above the rear view mirror, in the windshield frame showing that the air bag is off.
The Manual also describes where the switch is if you still can't find it.