Stain removal suggestions needed

[denzjos]

(04-06-2024, 01:55 AM)Danbor Wrote: Thank you so much denzjos! I've been trying everything I can think of to fix this image. Of course, since I don't know what I'm doing I haven't had much success.
I don't fully understand what you've done here but I'm going to attempt to reproduce it. It make take a few days, but I'll report back my progress.
  On a positive note, I'm sure learning a lot!

Edit:
   Ok, right off the bat, I'm lost. I managed the Colours / Auto / White balance step. But, just how do I select the color left from the sky and paste it as a new layer? And of course I don't know how to flip the layer and paste it to the right side of the photo.

First of all, right-click on the photo in the layer dock (small image on the right of your screen) end set 'Add Alpha Channel'
Correct this area :
   
Select this area and use it to correct the richt side (use the 'Free Select Tool):
   
To flip : Tools /Transform Tools / Flip (use vertical)
Use the 'Erase Tool' to get the small tree back