This solution is for people who have installed ReShade using the installer from this site. If you have downloaded a mod somewhere, seek help from its creator - this is not their support forum. If that's not possible, see solution 1.
1) The "Do it for me / I don't wanna read" solution:
a) Delete the entire game folder and re-download the game. No, just uninstalling the game will not work.
2) The "But I don't wanna re-download my game and still don't wanna read" solution:
a) Go to the game's executable folder and delete any of the following files you see: