Section A)

-> Locate Fairy Tail on Steam Library
-> Right Click "Properties"
-> Click on Tab "Local Files"
-> Click on Tab "Browse Local Files"




Section B)
-> Locate "game.ini" file and open it in notepad
-> Change to your desired resolution to play the game at.
example Width & Height 3840 x 2160 for 4K
-> In Notepad Click File & Save it.


NOTE:
If this method doesn't work, then backup the game.ini somewhere else and delete current "game.ini" the current one in the folder.

-> Try hitting Play to launch game again.
->The game should launch and create a new ini file automatically.
->If you can get into the game settings now, you should be able to select desired resolution.



EXTRA Info:
There appears to be other settings you can change manually as well, I have not tested or tried for myself the other settings.