Pursed lip breathing: Relax your shoulders, take a deep breath from your nose. Now make a 'O' from your lips, just like the way you whistle and breathe out slowly and for little longer than your 'breathe in' time. If you breathe in for 2 seconds, then breathe out for 4 seconds. This too can be done 10 times in an hour. This exercise creates a small amount of positive end expiratory pressure (PEEP). It supports the patency of airways and alveoli to participate in gas exchange.

Source: www.thehealthsite.com/news/shortness-of-breath-how-respiratory-physiotherapy-can-get-you-back-on-track-post-covid-19-822901/