Steering Adjustment Audi A4/A6 & VW Passat 3B

Hi,
"How do you adjust the steering on these specific vehicles? According to the repair manual, it's done via a screw from underneath (18mm socket), but I can't access it, mainly because I can only reach it with an extension, and I can't get it to turn. There's a plug in the screw; is there an Allen key or similar behind it for locking?"