PB
You've got your sympathetic nervous system, which is where your fight or flight comes from, and your parasympathetic nervous system, where your calm comes from.
The sympathetic nervous system responds instantaneously to perceived threats, you can get stalled in that mode if the stressor is chronic.
The parasympathetic nervous system takes about twenty minutes to kick in the calming biochemicals. There are various practices to engage it. If you can get yourself to focus on a single neutral or positive thing, a thought, a mental or physical exercise, it will help to kick in the those healthy feel-good chemicals. Repeat as necessary. If you can't get yourself to do twenty minutes, do it as long as you can.
Also, exercise will burn off stress hormones.
Combine with various calming dietary additions, as suggested by search.
You're here to grow a soul. View every thought, feeling, action as an opportunity to do that.