If you are a beginner to deep breathing exercises in general, it is best to start with the pursed lips breathing exercise.

To start off, you will inhale slowly through your nostrils. Then, purse your lips as if you are about to blow something and breathe out as slowly as possible, keeping your lips close together but not shut completely. The aim of pursed-lips breathing is to keep your airways open longer, thus optimizing the exchange of oxygen and carbon dioxide in the lungs.

Source: www.shoutoutuk.org/2021/02/12/boost-your-respiratory-health-with-these-expert-tips/