Choose your startup disk, and then select ‘Install.’.Once you see the macOS Utilities screen, select ‘Reinstall macOS’ and then click ‘Continue.’.Restart your Mac, while holding down the ‘Shift+Option+Command+R’ keys.If you’re on High Sierra 10.12.4 or later, and you want to revert to the version of macOS that shipped with your Mac, then you’re in luck! This is one of the easiest ways to downgrade your Mac:
