Perhaps I could use the retouch function in Windows’s Photos App to remove the lens flare in the picture
Personally I would rather use the clone tool in GIMP. (Press “c” for the clone tool. Then hover your cursor beside your lens flare, and press Ctrl and your left mouse button to get the portion of the picture you want to clone over your lens flare.
To brighten up a picture with GIMP, go under “Colors” in the top menus, and hit “Brightness-Contrast”.
BTW, awesome picture you got there!