Janos Karancz Trick

I can’t seem to figure out the trick from the 1.5 mount at about :58. Whenever I get to the slack part, I can’t get the slack right to go around the chopstick mount. Something with my fingers isn’t getting it right. https://m.youtube.com/watch?v=6l8mjHzjbk4

Press the string against your nth thumb to create tension

Nice