On Steam, use "Verify Integrity of Game Files."
Fallout 4 DLC files must be officially acquired and installed through Steam, PlayStation, or Xbox, with content appearing in the \Data\ folder on PC. Installation involves using platform-specific management tools, such as the Steam Library DLC section, console "Manage Game Content" menus, or by verifying ownership via "Restore Licenses". How To Install New DLC's / Add On's! In Fallout 4 Fallout 4 Dlc Files Download