During our time in Germany we would walk into the forest and breath deeply for a number of minutes. We didn't know of any techniques but it felt good and so we kept on doing it. Since then I have investigated a number of breathing techniques for different situation.
Deep diaphragmatic breathing facilitates movement of lymph through the bloodstream and dramatically increases the elimination of toxins, it also massages the intestines which may help prevent bloating etc. It’s simple to do.
The video below is a guided breathing session for beginners by Wim Hof