That trick is pretty hard if you are not used to do it on a regular surfboard.
Put the board on the trim line in a wave not too fast.
Lift the nose to put the board 90° on the lip and let the tail going first in the face.
Help your balance with the paddle.
Let the tail going first on the wave, like a take off fin first and manage that kind of take off.
When the fins touch again the wave, the second 180° will be done automatically.
Remember that you can to it with zero speed or at the opposite full speed…
SUPer : l’Ours on GONG and Drops gear.

Source : Team GONG SUP, in Drops we trust.