Where does confidence come from? Self worth.
How does one increase their self worth? By adding Value.
The more value we add to ourselves/ our lives in the form of skills, experiences and accomplishments our sense of self worth will naturally increase and by default provide us a greater sense of confidence.

Spend your time adding value to yourself until the day comes that you no longer walk into a room and wonder if the people like you, but instead you start asking yourself if you like the people. You'll know you've done the work once you start measuring every experience against the test of:
1. Do I align with this?
2. Is this worth my time?
3. Will this add value to my life or will this drain my energy?
4. Do I want to make room in my life for this person/ experience?