How Do You Replace That Feeling of Being a Piece of Shame?

If you have lost self esteem, your immediate reaction is, i'm worthless. That's known as a negative automatic thought. How do you replace that feeling of feeling like a piece of shate with, i'm ok. I'm happy with who i am. I'm comfortable looking in the mirror. And it's very similar to if you were exercising. Let's say you want to get into into weght lifting. What would you do? You might go on to youtube and look up some weight lifting videows. But simply learning about it isn't going to cause you to become more physically fit. You have to take that knowledge, apply it and literally pick up a few weights