An important aspect of finding your confidence is examining what you've done in the past that you now see as a mistake. Thoroughly understanding your prior errors is integral to developing your sense of self-assuredness.
Reviewing your mistakes allows you to say to yourself that you understand what happened and that you know now to approach those situations differently. Knowing what you did wrong and recognizing that you wouldn't do it the same way again builds confidence.
When you realize that you've gained some applicable knowledge, you also strengthen your confidence that you can meet any challenge in the future.