It takes making one re-write at a time, and you can do it!
The beliefs we hold about ourselves are stories, and nothing more. When they become hurtful, there are several ways to shut them down. You can try to stop your thought patterns with mental will power and mental exercises. You can change your environment, and this works by taking away your visual and sensory triggers that act like quicksand. Finally, there is anchoring new energy into your body with fartleks! Choose a moderate goal, move toward with gusto, and send that confidence into your root chakra! Not a chakra person? Send that feeling of worth and accomplishment straight to your heart, and let it go to work. I started with the shadow belief that runners were somehow better than me. They had more discipline, endurance, and confidence. My solution was to challenge that by running regularly and eventually entering a 5K. I began in the spring of last year, and yesterday I ran the Colorvibe 5K!
I changed the story by creating new sensory memories and lots of little victories. Your body resists change, but it is stronger than you think. The trick is interpreting what your body is telling you for the better. For example, when you start to jog, the feeling of your heartbeat raising can be scary. It can remind you of a panic attack, or other things that bring out fear, so start with this: I am not afraid of my climbing pulse. People who exercise all the time are used to this feeling in their bodies and some even crave it. You are changing your story. I am not afraid when my heart beats faster.
Another victory is one of your need to do it right. Too much speed. Too much strife. Too much inner whining which, by the way, is dis-satisfaction with yourself. Treat yourself better. Allow a comfortable pace to evolve. Allow others to run faster. Allow yourself time to achieve your goal. You see, the mini-victories are at work on you all the time. New energy is being integrated into your body and lifestyle. New memories are being formed in your cells. This is manifesting like a master.