Step 4: In case Fallout 4 is already installed, then you need to find the game and confirm the location by selecting the check box. Step 3: Once the installation process starts and completes, launch the Nexus Mod Manager to scan the computer for games that the app supports. Step 2: Register with a free account with the ‘Create Account’ option. Step 1: Access the site: and download the files depending on the operating system.