Scar (or pigmentation?) on the chest after skin-picking. (photos)

Hello, Dear Doctors! I have had a skin-picking disorder for a several years. Three years ago I picked up skin on my chest because I thought there is a black head but there wasn't anything. Usually I picked up skin on my face and I never got scars or spots. I thought with chest will be the same. But I was wrong. I never picked my chest again so it is the only one selfmade spot I have on it. How can I get rid of it? I am trying now azelaic acid 15% but it just make it red, don't peeling away.

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