The higher res the image the better so this can be difficult in this case. What you need is the inverse of the light patch and then add it in. If its too light (or dark) then you can find that the lightened areas have saturated to the 255,255,255 color and its hard to reverse. So if you still have that light patch as a brush or image that you can get at (say its a VTT token) then get the inverse of it and blend that in. Recently I demoed removing a watermark for somebody which was mostly successful. You could still see the outline which is why higher res is better and I was not given the mark to invert so I had to make it. I used that inverse with dodge and burn to get the amount right for the blend.

If what your trying to remove is of colors very different to the background or it has a fixed pattern thats very different from the background then its much easier. Stuff with noise on the top is very hard automatically.