Welcome @Playtos. 
You will need to use the Epic Games trainer for the game if you have bought it from the Epic Games store. The trainer that you are commenting on is intended only for the Steam version.
The Wintermute DLC has not been released on Epic Games yet. Therefore, it is not possible for Wand to acquire a copy of it, which is required before a trainer can be made for it.
See: The Long Dark Cheats and Trainer for Epic Games - #54 by Ravenfyre