This sounds like a fairly simple procedure, I have the skills and availability, and am in the USA, making it easier to communicate instead of through timezones.
I'd love to see the photo and learn a little more about what you need doing with the sunset exactly, it's hard to say the exact process, but there's a swathe of tools in the Adobe Creative Suite to use for this. From color manipulation, selective region editing, super imposing, to background swapping, addition, removal.
Let me know your needs!
Best Regards,
Jacob Dodd
Business Animator