I’m a swimmer too. 1 mile each time, 4 times a week. Sounds like you can swim, just not very long

If that’s the problem I don’t think you need a private coach. Just keep swimming like Baron said in his post. I believe you will swim 1.2 miles eventually. Since you try a triathlon, you must be a capable distance runner. That’s a plus. Swimming and distance running are similar in that you may feel some difficulty in the middle of the process. But that difficulty will be gone. You will feel much better in your last third of the course. I have a lady here who is 71 years old. She swims regularly, 2000 meters each time.

Can you do a flip turn? 1.2 miles swimming in the pool needs a lot of turns. You may need a private coach to teach you about that if you can’t. But you can still learn on your own. It’s not very difficult.

Don’t panic. Swim relaxed. Tense/nervous can make you tired.