Keep in mind that tensioner assembly is the same that will be in any 06 to 08 GTI or Jetta with the FSI 2.0t engine (same exact engine).
And VW dealers can sometimes be a bit better on price since the Audi dealer seems to think they sell Ferrari's or something lol.
It will more than likely be the tensioner unless the belt is very dry but regardless you should change both.
This fix is very simple
There will be three 13mm bolts holding the tensioner to the engine (green arrows, keep in mind there is a 3rd one not visible in the pic)
Take a wrench (should be about 17mm) and put it on the bump on top (Blue arrow) and pull the wrench toward the radiator to twist the tensioner so that the hole in the front of it (left side red arrow) alligns with the hole in the rear half of the housing (right side red arrow) you will need a drill bit or something to put into the hole to pin the tensioner in place.
The belt will now be loose. remove the belt and then the 3 13mm bolts holding the tensioner... Assembly is exactly the opposite