that is used as a way to push the logic board out the back. all you do is
1. make sure the back of the mac mini if facing you.
2. make 100% sure that you have got all the screws ( the tear down missed some screws).
3. make 100% sure that you have disconnected everything (i broke the clip to my IR sensor by not paying attention)
4. put two screw drivers in the holes and pull towards you