Angband already gave the best answer, a direct link to methods.

But, yes. There are multiple options for improving one's airflow. The first and most important is to get evaluated to rule out anything that needs to be directly treated.

Since there's already a link, I'm not going to waste time with that side of things. What I will waste time with is sending respect his way. Taking a multi pronged approach to improving health is the ideal way. But it's harder. It takes applying self discipline across every aspect at once. However, it also gives you cushion on each individual one because you don't have all your eggs in one basket. So, if a cold prevents breathing exercises, diet will still be working. If he has a day where ideal eating isn't possible, the exercise still improves other aspects.

And it is absolutely a fact that improving health isn't purely about excess fat. There's synergy involved with exercise, improved diet, and other lifestyle changes. Each one makes the rest easier and more effective.

The key is in not going too hard, too fast on any of them, except maybe breathing exercises, because there's really no drawbacks to pushing hard on those, within reason. But if you push your body too much in early stages of new exercise, you risk injury, and you'll end up burning out. Same with dietary changes; that's the mistake a lot of people make. They try to totally revamp their entire nutrition plan at once, and then wonder why they struggle. There's a learning curve to nutrition, and another curve to diet.

And yes, nutrition and diet can used as separate terms; nutrition being the understanding of what your body needs, and diet being what you put into it. See, even once you develop a deep knowledge of what you're supposed to eat, you have to implement it. People think it's as easy as just buying the right things, but it absolutely isn't.

Most people needing that kind of change also have built up metabolic dysfunction, built up tolerances to sugars and salts and fats and carbs (sometimes even protein, but I don't see that as often for some reason). You have to change those patterns, change the way your brain expects to feel after eating, change the way insulin is signalling you, etc. Changing that all at once, without any kind of plan for it is just not going to work well. And then people are left wondering why they either fail to notice improvements in health, or just give up because they're constantly stressed fighting their own body and brain.

So you have to approach that curve just as aware of the difficulties as you do when trying to learn anything. It's like climbing a rock wall. You have to choose your approach and think ahead of the step you're on.

So much respect for your neighbor, and anyone using a multifaceted approach to their health journey.

Tell him to keep at it, look into the breathing exercises linked. If walking for his main exercise becomes a problem, it's okay to switch to seated lower body exercise for a while. And don't let small setbacks blind him to the forward progress! It's easy to get frustrated when you have a bad day and think you're never going to get better. That's only true if you stop. Slowing down is still moving forward.