Adding Pre-Tensioners?

HI,

I've got an aftermarket VCDS lead.

The airbag light's on and we think this may be to do with the seat belt pre-tensioners showing as 'not installed. There are pre-tensioners present for the front ones, so I think I just need to tell the car that they're there.

Can anyone tell me how to do this? I don't know much about VCDS, but I think this is probably something someone will know. Hopefully not too hard for me to do myself.

The car's a 2001 y-reg Skoda Fabia 1.9 TDi