There's a few things here. First of all - there are no rescue swimmer / officers. That's an enlisted job.
Second - If you want to actually rescue people - join the Coast Guard. USAF swimmers are mostly recovering bodies from crashed planes. Third - Why the heck would you ( a terrible swimmer) want to do this?
But.... Go to your local Y , sign up for adult swimming lessons. Watch videos on technique etc. Swim a lot of laps , swim underwater to build your endurance. Swim legs only , on you back - while carrying something, Take the Y or Red Cross Life Guard training ,
But, I still think you're nuts.