This exercise is called the four smiles exercise.
Basically all you do is take a moment, let your mouth soften into a smile, then expand that smile for each of the next three breaths. First, expanding it so you feel your whole mouth, not just your lips, but your whole inner mouth soften and rise into a smile. Your forehead, your throat, and you keep feeling that smile expand until you feel it in your heart. That literally takes four breaths and you’re feeling a lot more buoyant.