I have to call pass on that one. I think you/we don’t need one and that it should be a question of connecting the wires and playing with settings.... unfortunately, they have been played with on mine by a previous owner so I need to pull the airbag out again and work out what has been done before I can tie it into the head unit.... I’d be interested in what you work out.....
As far as the head unit side, I think it’s the three brown wires in the bundle with the ISO connectors, think they’re marked as Key1 Key2 and something else.