Go to https://reshade.me/ and download the latest update.
Install the RDR2 PhotoRealistic Graphics.ini file into the RDR2's game directory

Steam Directory: Local disk, Program Files (x64), Steam, steamapps, common, Red Dead Redemption 2

Epic Directory: Local disk, Program Files, Epic Games, Red Dead Redemption 2

After loading into the game make sure to press the HOME button located on your keyboard and look for the drop down menu, then select RDR2 PhotoRealistic Graphics.ini
and your finished!