I've found how to do this on my car recently (a guy doing my seats set the airbag light off) - access the Safety Module using INPA, find the error by reading the codes on one of the 5 different sections (curtain left, right, driver airbag, etc.) and one of these will be the issue. Just reset it and the light should go off.
When I had dazols around my house a few months ago trying to reset his light, I couldn't access his Safety Module using my INPA, but on my 2004 car it was fine. Maybe it is trial and error, or a software thing...