I don’t think there is just ONE book or even 2 or 3. But many, I posted my favorites having started this in the early 80’s
That said, if you read them closely, you will see common themes among all of them about training, riding and competing, managing them and our own riding aspirations.
There is a common thread in all of these if your read really, really closely.
Just have to find them, study, work at it… and make them work for you and the horse in your charge, which may all be a bit different from prior handling. Let that go and just go back, back, back and study all this.