Fake it until you make it. Better stated, imitate self-confident successful golfers. Identify the people around you who seem to have a good degree of self-confidence, and watch what they do. Is it how they work, what they say, how they carry themselves? Select one small behavior at a time and try to emulate that. Imitation can be a route to learning. Pretty soon you will begin to feel confident too! If not, then examine and be ready to adjust your underlying beliefs.