Physiological sigh
This technique of a double nasal inbreath, followed by a slow outbreath through the mouth, can help calm us down in the moment. We naturally do them when we're stressed, and voluntarily using it as a technique can help to calm us down.
What they say
Overall, the physiological sigh is a powerful tool for both mental calmness and physiological benefits, making it valuable in various stressful or anxiety-inducing situations: Andrew Huberman on the Physiological Sigh, here