@isazi Oh thanks for your warm words 🙏, when you want to learn from a teacher I suggest to look for a local teacher. Often this can be learned in Qi Gong courses or also in Yoga or Tai chi classes in fitness studios or martial arts schools.
Qi Gong is often the easiest way to start since it has easier movement techniques (compared to Tai Chi or Yoga from which I know very less) and breathing is an fundamental part of it. There are “low quality” courses who only teach the movement, like a gymnastics style, but breathing is an integral part of all “inner arts”.
If you just want to practice breathing by yourself, there are many books and even good apps. I could recommend the books from Dr. Yang Jing Ming, a highly skilled and respected master like this:
https://www.amazon.de/Qigong-Meditation-Embryonic-Jwing-Ming-Yang/dp/1886969736
which is also available as an app for Android an iOS with good videos.
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Or better for starting:
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Dr. Yang has a lot of good publications and being a physicists he also has a scientific background. He also has many videos on YouTube.
Another great book (but more on Qi Gong / Chi Kung as a whole and the Zhang Zhuang “standing like a tree” techniques) is “The way of energy” from Master Lam Kam Chuen, which I consider the best book for starting to practice Qi Gong since it is very well written and covers every aspect of life and how practicing Qi Gong techniques help e.g. to have more stamina in sport or in all day life.