just exercise. it will be ok, really. somehow we managed for millions of years, kiddos, and both gravity and the human body are unchanged in any relevant way since which suddenly requires "an app". I can get out of bed without an app, or an AI. I can prepare a meal and eat without any kind of app, or any kind of AI or LLM. its a true and real thing, in the real world, promise!
There are tons of different conditions people are in, with different histories of injuries, etc. and even people without any issues benefit massively from having a sensible, well structured workout plan that ensures their weaknesses are addressed and they work towards their personal goals. You don't need AI, an app or a personal trainer for that but while many people do enjoy learning a lot about exercising in their (often limited) free time, many don't and it's great if they have an affordable/free option. Why do you think physiotherapy exists?
Additionally, studies have proven that progressive overload is a really important aspect for progressing, so you should be tracking your workouts in some way, in an app or on paper, to ensure you really are challenging yourself.
I would have loved to have all that in an app over the last 25-30 years so I could see my progress.