Reflect on things- think back frequently and regularly. Did you make good decisions with what you knew at the time? Did you act decently/ wisely/ with integrity? What are your moral values and do you strive to live them in daily life?
Do you then learn when things go wrong or you didn't do something as you would have liked to ? or when you do something that has bad consequences- for you or others?
Reflect and learn. Then you can demonstrate to yourself that you're a decent/competent/ thoughtful person.
Then, over time, you just gradually develop awareness of, and confidence in, your own abilities and judgements and don't need other people to validate you.