For installing this file you should download the .rar file from "Resources" page and open it with WinRar. The save file should be put on this path:

C:\Users{your user name}\AppData\Local\ArkhamVR\Saved\SaveGames

P.S. Usually AppData is hidden from the user, to locate it you must press Win+r and type "appdata" in a window that opened. Press OK and you will be right in a file

P.P.S I recommenr to use it on Any% too, without "Riddler progress options" because the load screens won't be so long and you shouldn't press the button on piano