Face and confront this voice. In CBT there is a exercise called ABC that my T told me when I first started. Basically, you have to write down your anxious thoughs that emerge in different situatons (example: I'm at school, I start to think "my classmates will laugh at me or nobody will talk to me; these are anxious thoughts, because they led you to become anxious, maybe you'll start to sweat, or to shake, and you'll avoid things). Then when you recognize these thoughts you confront them, you ask yourself "are they really true? Are they realistic? And why? ".