Follow these steps to add a customized character to your game:
Create a new character BP
The player blueprint used by default is BP_HEPlayerCharacter, located in RetroHorrorEngine Content/Player. Create a new BP using BP_HEPlayerCharacter as a base class
The player anim class is compatible with UE mannequins so you can easily replace the character with a mesh using a compatible skeleton
Create a new GameMode
Remember to create your GameMode, using BP_HEGameMode as the parent class and replacing the Default Pawn Class with your new BP.
Set your new game mode as the default GameMode in your project settings
Bear in mind this will not replace the game mode in some levels where this has been overridden. You can change this back to default on the WorldSettings or change it manually to use your new game mode in specific levels.