This is something that you can do any time you need to reset your nervous system. Any time that you need to down-regulate, or any time that it would be helpful to safely step out of a place of stress.
Take a deep breath, and close your eyes.
Imagine, experience, or pretend a place where you feel totally and completely safe.
(And if you're not in a place to make that happen, you could also try finding a place where you feel pretty ok.)
Just breathe. Just be there.
Spend 2-5+ minutes here.
And touch your heart.
Any time you need to return to this place, you can easily do so just by touching your heart.
Here's a longer version of a recording that I made a while ago.