Adding a Linked Project

When you split a project into smaller projects or when you extract smaller projects from your main project, you have the option to add the extracted projects to your main project's list of linked projects. To do this, simply check the Link extracted project checkbox at the bottom of the Split Storyboard or Extract Storyboard dialog, and every project that is extracted from your main project will be automatically added to the list in the Project Management view—see Splitting your Project into Two Projects or Extracting Parts of your Project into Other Projects

If you need to add an already existing project to your list of linked projects, you can do so in the Project Management view.