Update. Steering assist cannot be adjusted on mk6. Inde Tech guys spent more than an hour and failed.
Unless someone knows how to change my Polo into a GTI again I will have to reject the repairs and the car. It's not just the steering that's wrong. The whole "repairs" are just shocking (a collection of completely random screws under the bonnet, I'll put a photo tomorrow), Park assist, sensors and camera in "Park assist fault. Workshop!" mode and on top of that the VIN on the chassis is gone. Any solution offered by the repairer (re-stamping using ebay bought tools, welding a plate with said stamped VIN) is likely to make the car unsellable. I think I've seen enough of this good garage...