You really need to just practice this whenever. Trying it out in the moment is like to be too daunting of a task and you’ll incorrectly convince yourself that it doesn’t work. This podcast explains the science of why you probably actually aren’t running out of air https://anchor.fm/tim-mackesey/episodes/Breathing-and-speech-How-do-we-breathe--If-I-stutter--when-and-how-do-I-breathe-ee2611