Hello,
If merging doesn't work, in the DLC, you should find the folder dlc_muzzle:
Copy it and paste it into the game's folder, at this location (the root folder won't be named CT_EARLY_ACCESS... but something like demonheart-the-cursed-trial...):
When the game detects it, a checkbox will appear in the settings like this (you'll need to turn it on):
I hope you'll get it to work, and I will try to change the instructions on the game page to clarify.