Tuttifrutti

Good evening all, Hopefully you can advise me? I have a colour image with a totally bleached out sky. I want to select the sky and darken it in some way to see if there are any clouds at all I can find, that would add interest to to top part of my image . It's a church scene. I've found out how to select the edges of the rest of the image but i'm stuck as to how I then darken the selected area. Please can someone help. Many thanks