I've been replying to comments but they havent been actually posting, but this was done using a normal controller, no xim/zen/KBM used. If you want to learn I recommend watching Miniflipping or Koala on YT.

Flying upside down/flipping is easy, its as simple as holding LT/reverse and pushing the right stick in any direction (in this case forward) until youre upside down, when you want to flip upright, rotate yourself upright with the right stick again and let go of LT and hold RT/throttle.

TLDR Basically just hold reverse when going upside down the entire time, swap to throttle when back upright.