Girls, hi. My daughter had red spots on her back before. I read that i…

Girls, hi. My daughter had red spots on her back before. I read that it's a rash and will go away by itself. Now there's such a bump with a crust. I don't understand what it is. She's alone, nowhere else, it doesn't grow or shrink. Has this happened to you? And how is it treated or will it go away on its own? We're going to see a pediatrician soon.