Self-confidence is grounded in reality. You can only develop self-confidence by doing things in real life.
You can read countless books about flying, inform yourself about every plane and go through take-off and landing in your mind. In this way you try to prepare yourself passively for something that you want to do actively later on. So, can you fly then?
Self-confidence is the result of trust in yourself. And that is the result of courage. Only once you have had the courage for the first real flight do you develop the self-confidence for the upcoming take-offs. Without the initial courage this is not possible.
You will never feel confident enough to do something that scares you. But you can be brave. You can do a thing that scares you and feel self-confident afterwards.