Most of us dish out more put-downs to ourselves than we realize. They come so easily! Perhaps you were told "you are not okay" in one way or another when you were a child. These messages are still with you. Now, they must be counterbalanced with positive messages. You are the one to do this. Maybe you were taught not to think highly of yourself. Give yourself permission to look for and validate your positive attributes and your successes. You can speak as a nurturing parent to yourself, even if you did not have one in real life.
You also need to catch yourself being negative about yourself. When you hear one of these messages, pause and focus your attention on what you are saying to yourself. Awareness is the first step in change. Let your nurturing parent rephrase that remark. Feel the acceptance. Have a conversation with yourself, right now. Begin with "_____________(your name), I understand why you have _____________(former failings). It's okay, and you are loved."