Select the game from your library and scroll down - your content will be displayed in the Owned DLC section of the overview.
Pieces of content with an Install button displayed next to them are not yet downloaded. Click it to start the installation process!
Select the game from your library - your content will be displayed on the right-hand side of the overview.
Click Manage My X DLC to open an additional window where you can see which content is already installed and enable/disable it as needed.
Epic Games Launcher
Find the game in your library - your content will be displayed as a number in the top-right of the tile.
Installing the game will automatically download and install all available content for the game.
Do not hesitate to let us know if you have any other questions!