Self-confident people share one habit in common, and that is the ability to keep the promises they make to themselves.
Ed Mylett
Many people have a view of how to gain self-confidence. This is the best way I have heard it defined.
The truer we live to ourselves and develop self trust, the more confidence we gain being ourselves around others.
Start small, it could be as simple as baking a cake from beginning to end, going for a one-mile walk; see something through to completion.
Start with small wins and keep building to larger things.