Hi. I had exactly the same problem on my 2014 Q7. I purchased a new part from Audi. I asked them about how to fit it (of course they declined to provide any clues). But from using the new part I was able to work out how to change it without removing the bumper. So the bumper does definitely not need to be changed. Here is a few comments on the process followed:
1. Removed both screws - I loosened them with grips on the thread side and then reached in and removed completely with fingers.
2. The light now wobbles but will not come out because (a) the brackets for the bumper, stop the brackets for the lighting unit from getting past (as the bumper brackets are in front of the lighting brackets), and (b) There are two clips on the top of the lighting unit that slot into the bumper itself (you cannot see these until the lighting unit is out).
3. The lighting unit needs to slide out from the slots in the bumper (to address comment b. above). In my case, the light needed to be pushed back and slid towards the outside wing of the car). At this point you can leverage out the clips on the top of the lighting unit with a flat bladed crew driver - just place it in between the lighting unit and the bumper and lever it down. This did take quite a lot of force...
4. Once the top clips are free, the lighting unit can then be rotated (top edge comes forward) and pulled out over the top of the bumper brackets (thereby addressing part a. above. The unit should now come out.
To be fair, it did take quite a bit of force to get it out, so be brave...once out, just reverse the process to put the new unit in. I hope this helps.
