Working on your breathing is a way to help release the tension in the chest, but can also let your body know that you are safe. If you are able to take long, deep breaths then the body gets the cue that you are safe. Try the following breath work exercises:
Taking longer, slower breaths
Box breathing (inhale for a count of four, hold your breath for a count of four, release your breath for a count of four, hold your breath again for a count of four, and continue)
Diaphragmatic breathing (put your hand on your stomach with your pinky finger just above your belly button and breath so that hand moves up)
Long breaths out (have your breaths out be twice as long as your breaths in)