Downloading and Installing Xcode Components
Download and install optional tool components using the Components section of the Downloads preferences pane.
To improve download time and installation efficiency, the standard Xcode installer excludes some large tool components, such as older simulators, that are not essential to the current development toolset. If your project requires such optional components, you can download them on demand.
The Components tab shows a subscription entry for each optional component. When an optional component is available but not installed on your system, Xcode displays a Download button on the subscription line for that component. Click that Download button to download and install the component on your system.
For your convenience, Xcode can automatically keep optional-component subscriptions up to date. This feature is controlled by the option “Check for and install updates automatically.” To check for updates manually, click Check and Install Now. If no new updates are available, Xcode displays a message to that effect.