The only way to turn off this light is to take it to some one that works on airbag systems. That light is on because of a system malfunction, it could be one of the bags themselves, one of the impact sensors, the computer that controls the whole system. Or the wiring between all of these.
I had a similar issue. I brought mine (2006 A6 4.2L s line) to the dealer and they determined it was a faulty airbag sensor in the back seat. The light indicates a fault somewhere in the airbag system. The fault can prevent the airbags from properly deploying in a crash and should be checked and repaired ASAP considering no one ever plans on having an accident nor do they occur when it would be more convenient.