I'd like to know how to change the air in swimming. Please see the supplementary instructions for details.

I don't know if you can understand it. Before you take a breath, you put your hands and fingers together and push down, which feels like the action of lying down and holding your head up, so that your head will be higher and you won't sink immediately. Breathe through your mouth, inhale as much as possible, sink after inhaling, and then exhale underwater.