Here's what I did with the tutorial. I could improve it more, but honestly... I don't feel like spending the time on an image that was uncensored to begin with.
But, it goes to show you that a lot can be done. Also, I did not use any part of the original image to fix the middle picture. (in case you were wondering).
One other tip: Did you know that lips are the same type of color and texture as nipples? Well, in many cases you can select lip color to restore nipple color. I applied a bit of that here. It doesn't work well if they are wearing lipstick though!
Once again, this is a very basic example. There are many other tools to draw upon. But I thought a straightforward display of proceedure might be helpful to those of you who are interested in giving this a try.