Below are several video links to a few different styles of breathing. Ask your physical therapist which style might be right for you.
Wim Hof breathing
This practice involves rapid breathing followed by breath holds of varying lengths. Not a great option for someone who is a hyperventilator, but for those with normal levels of CO2, this can be a very powerful and healthful practice. I've included a link to some of the research regarding the Wim Hof Method below.
5.5 breaths per min
This practice involves equal inhales and exhales for 5.5 seconds each. To learn why this breathing style is so powerful, check out James Nestor's book, Breath.
Box breathing involves equal parts inhale, hold, exhale, hold, then repeat. Choose whatever time interval suits you. This particular video is 5 second intervals and goes for 10 minutes. There are plenty of other videos on YouTube with other time intervals and for different lengths of time if you prefer.