Hi I received my car back from a body repairer with the airbag light on, it wasn't when I handed over the car although they have said it was after I called them (Rear bumper repair they said error couldn't be caused by them fixing) . I cant get mot (uk) had another garage run diagnostics but they couldn't reset srs error so didn't do mot as its automatic fail. The error they said was the error listed in post title. Apparently the left side (passenger) airbag system error.
Some things that may be important
1) passenger seat was pushed back completely when I got car back, no need for repairers to be involved in this area if fixing rear bumper. Could this have caused the error?
2) the car was idle for a couple of months prior and required jumpstart. Repairer said the backup battery just needs reset to turn off airbag light. Is this possible/correct?
3)the car has water damage in front area, could this be cause?

I'm sorry for the long post but I'm at the end of my tether and have not been able to use car for months.
any advice would be greatly appreciated, thanks