If you want to get rid of the warning light you can put the car into "diagnostic mode" and it will check if the warning light is still valid.
If you have the airbag light, it will show steady for a few seconds (the manual says 7 secs) after you turn the key from off to on (but not start) and then start to flash. Here is how to reset it:
1. Turn the key from off to on.
2. Watch the airbag light closely. It will stay on for a few secs. and then as soon as it blinks off (the start of the flashing), turn the key off instantly.
3. Count to 5 (1 Mississippi, 2 Mississippi . . . .)
4. Repeat steps 1-3 two more times until you have done the cycle three times.
5. Now turn the key on and watch the light. It will start blinking in a different, slower manner. This is diagnostic mode. You can watch this for a little while, no hurry.
6. Now turn the key off again, Count to 5 like in step 3 again, and turn back on. If the procedure worked, the airbag light will not be flashing.
If it does not work the first time, just repeat the steps again.
Source:
http://www.nissanforums.com/frontier/142419-air-bag-warning-light-comes-need.html
It worked for me when I had some stuff under the passenger seat and managed to disconnect some wires. Plugged them back in and did this and that sorted it. Hopefully should work for your friend.
