honestly, there are guides on youtube that explain it better than i could
jogging is always good
and you're referring to freedivers, they are machines when it comes to this... they do this thing called lung packing, which is when you take a deep breath, and then basically force more air into your lungs by swallowing it, and holding it until they get hypoxia. rinse and repeat....
it makes sense if your goal is to larp as dolphin, but otherwise just exercise, avoiding smoke and dust, and normal breath holding is all you need