The breath is a powerful tool for engaging and manipulating our nervous system. Specifically, using a slower exhale than your inhale has been shown to engage your parasympathetic nervous system. This specific breath is useful for anxiety and stress. You inhale for a count of 4, hold for a count of 7, and exhale through your mouth audibly for a count of 8. Full instructions alongside a video can be found below:
https://www.drweil.com/videos-features/videos/breathing-exercises-4-7-8-breath/