The adjustment is on the pump timing pulley. Here's a photo..................

Ideally you'll need a VW cambelt timing tool set. They aren't expensive, but you can do it without.
It's more than ten years since I did this job, but from the AEF manual.................
When you can insert a 6mm (or could be 8mm?) dowel through the hole in the pulley boss , and into the hole in the hub, the pump is set at exactly TDC (like the one in the photo). You can use the plain end of a drill bit.
Obviously if everything is OK, then the crank will be at TDC as well. If the crank is at TDC you'll be able to insert the crank timing tool. (Or you can look through the hole in the bellhousing for the mark on the clutch cover). If it's not, with the pump locked as above, slacken the three bolts holding the pulley on to the boss one quarter turn max NOT THE CENTRAL NUT!!!!, and move the crank until it's at exactly TDC. Now tighten the three bolts to 25Nm, rotate the engine two turns by hand in a clockwise direction and check it all again. You'll have to counterhold the pump pulley to slacken and tighten the bolts. I use a piece of metal with two bolts through it.
You will be able to tell if the timing has been altered, because just like in the photo, you can see the shadows of the original bolt positions, so naturally the bolts should cover the shadows exactly.
While you're in there you might as well check that the cam is at TDC as well. The tools to do that should be part of the cambelt timing kit. Plenty of instructions on here and t'interweb for that job.
I've never needed anything but the original factory setting. I figure they would have got it right!
Top tip for this job is to attach a long length of bright ribbon to the dowel, to remind you it's in there, just like aircraft techs do.