Leaders ask me (usually privately) how to increase their confidence. It's been my experience that people build their confidence by taking action and experiencing both success and failure. The common denominator is that confident leaders tend to be those who confront the challenges in their workplaces, learn from the process and increase their self-awareness along the way.
Eleanor Roosevelt said, "You gain strength, courage, and confidence by every experience in which you really stop to look fear in the face. You must do the thing which you think you cannot do." It is the action of doing things purposefully toward your goals that will help you become a confident leader. You have an incredible ability to take on any challenge in your workplace starting today by focusing on what you can do.
Try taking on a challenge today and keep doing it until you are an expert. Put one foot in front of the other and keep walking. Then take on another challenge and keep going. In time you'll wonder why you ever lacked confidence at all. What will you do to increase your confidence?