Beliefs define our identity. If you believe in something long enough, it becomes part of your identity. It can be a good thing or a bad thing based upon what you believe in.
If you think you're a confident person—even when you're not—you eventually become a confident person.
But just having the belief isn't enough; you have to internalise that belief and let it become a part of your identity. How do you do that? It's not very complicated. Let me tell you a little about it.
Let's say you want to be a disciplined person. You have to start with the belief that you're a disciplined person. Then you have to start behaving like a disciplined person, and how do you do that?
Whenever you want to do something that requires discipline, you tell yourself that you're a disciplined person and you do that task forcefully. When you keep doing it again and again, you eventually become a disciplined person.
It's basically faking discipline until your brain actually starts behaving like a disciplined person.
This has worked for me in terms of confidence. When I don't feel confident about anything particular—I tell myself that I'm a confident person and start pretending like one—I succeed in convincing myself and others that I'm confident.
What you tell yourself matters a lot. What you think about yourself matters even more. If you think anything negative about yourself, you will start exhibiting those negative traits.
So, why don't you change your perspective on yourself and start believing in positive and good things about yourself!