1. Restart your computer by pressing thepower button.
2. Immediately after releasing the power button, press and holdCommand R.
3. Keep holding Command R keys until you see anApple logo or spinning globeand thenreleasethe keys (this might take a few goes).
4. You may be asked to select a Wi-Fi network. To select a Wi-Fi network, use the Wi-Fi menu in the top right-hand corner of the screen.
5. When you see a window with the option to reinstall macOS, this means your Mac has started up from Recovery.
6. ChooseReinstall macOS and clickContinue.
7. If the installer offers the choice between installing on Macintosh HD or Macintosh HD – Data, choose Macintosh HD.
8. Follow the install prompts.
9. When installation has completed, your Mac may start up to a setup assistant. Follow the steps in the setup assistant.