Most "trainers" can be buggy or trigger anti-cheat, but the community standard for this game is (or similar Steam API emulator configs). It tricks the game into thinking you own the Steam AppIDs for the DLCs, even if you just have the base game (or the Epic Games free version).
For those playing on Steam or Epic Games Store, "APIs" are the most common tools. These files are placed in the game’s directory to bypass the store's ownership check. world war z dlc unlocker best