Watch the video then complete 45" second nasal diaphragmatic preload breath work and AMRAP - as many reps as possible and then recover for 45" with nasal diaphragmatic breathing. Do 3-5 total rounds.
Negative breath works is a powerful tool for raising endurance, comfort, and confidence in your breath.
The approach shown in the video is meant to mimic the mental and physical challenge of unexpectedly getting your breath knocked out. As in catching a rail or a wave hitting and knocking you down then having to swim to the surface or being dragged by the waves power for awhile.
Becoming more comfortable with this scenario takes practice and this simple Negative Breath Work program can be done as part of any other movement work you are completing.