Welcome to the community forum @davidharvey24. 
As the name of the trainer suggests, this trainer was designed specifically for the Steam version of the game. There is no guarantee it will work flawlessly, if at all, with other versions of the game.
For the Epic Games version of Batman Arkham Knight, you need to use the trainer that was designed specifically for the Epic Games version, which is here: Batman: Arkham Knight Cheats and Trainer for Epic Games