Your brain is an intricate network of patterns. What you say about yourself or what you hear about yourself consciously or subconsciously affects that pattern. That pattern becomes the story we believe about ourselves. In this space you can choose to rewrite that story. Write down positive traits about yourself. They can be true or they can be aspirational.
If you need help getting started, slide through some affirmations.
Read them out loud for the best effect on your brain.