Have a 2006 GMC 3500 the service airbag light stays on, how is that fixed?

Welcome to the forum Al!
If the air bag light is on there is a stored code so...the best place to start is by having a shop read the stored codes by a Tech II or capable scanner. I hope that it may be something simple like a connection problem or sensor. The code should hopefully point the tech in the right direction. If you are able to post the code or codes in here I am sure our techs/gearheads can assist further.
Hope this helps!

I know OnStar can look at engine codes, perhaps they can look at other system codes as well?