There are so many that I don't know which to recommend as I've kind of learned the stuff and do it on my own now. It's a little time-consuming but best if you search them on your own as some are designed to address specific issues. For example, when covid hit, I looked up videos for exercises specifically using 'the bottom' of the lungs as it seemed from articles that people with a diminished usage of lung capacity (not diminished capacity, but diminished usage) were having the worst results and then ending up on respirators and things went downhill fast.

So friends and I were all doing deep-deep breathing exercises to try to achieve maximum use of lung capacity.

If you even start with simplest yoga, paced deep breathing and go on from there, that's the big first step. I find that I get what I think of as 'air hungry after a few minutes of doing that and breathe more deeply, automatically, for hours after. Shallow (diaphragm breathing) just feels wrong. There are also videos using inexpensive breathing-aid gadgets that might be helpful.

It's always best to check with your doctor before trying anything that's not easy or can interfere with any condition including blood pressure though.