You can use macOS Recovery, the built-in recovery system on your Mac, to reinstall macOS. macOS Recovery preserves your files and user settings during the reinstallation process. (check Apple Support Article about macOS Recovery)
Important: Your computer must be connected to the Internet and to a power supply to reinstall macOS.
Start a computer from macOS Recovery :
- Choose Apple menu 🍎 > Reboot, then immediately press and hold one of these key combinations, depending on what you want to do:
- Reinstall the same macOS Version: Command (⌘)-R will restore the same version of macOS that was on your machine.
- Reinstalling the most recent macOS version (compatible with your Mac): Option(⌥)-Command(⌘)-R combination will put the most recent macOS compatible with your machine.
- Reinstall the original system: Shift-Option (⌥)-Command (⌘)-R will restore your Mac with its original version
- In the Recovery app window, select the Reinstall macOS option and click Continue.
- Follow the instructions on the screen. In the pane for selecting a volume, choose your current macOS volume (in most cases, it's the only one available).