Use macOS Recovery to reinstall the Mac operating system.
How to reinstall Mac OS?
Start from macOS Recovery
Reinstalling the Mac operating system requires an Internet connection. So first make sure your Mac has an Internet connection. Then follow the appropriate steps based on whether you're using a Mac with Apple Silicon:
· Apple Silicon . Apple Silicin
Turn on your Mac and press and hold the Power Button until you see the Startup Options window. Click the gear icon labeled Options, then click Continue.
· Intel Processor . Intel Processor
Turn on your Mac and immediately press and hold Command (⌘)+R until you see an Apple logo or other image.
If you're asked to select a user for whom you know the password, select that user, click Next, then enter their administrator password.
Reinstall macOS
Reinstalling macOS does not remove data from your Mac. To start the installation, select Reinstall macOS from the macOS Recovery Utilities window, then click Continue and follow the onscreen instructions.
MacOS Recovery Utilities window
Follow these instructions during installation:
How do I reinstall Mac OS?
If the installer asks you to unlock your disk, enter the password you use to log in to your Mac.
If the installer doesn't see your disk, or it says it can't install to your computer or volume, you'll need to erase your disk first.
If the installer offers you a choice between installing to Macintosh HD or Macintosh HD + Data, choose Macintosh HD.
Allow the installation to complete without putting your Mac to sleep or closing its lid. Your Mac may restart and a status bar may appear several times, and the screen may be blank for several minutes at a time.
After the installation is complete, your Mac may restart with a Setup Assistant. If you sell, trade, or give away your Mac, press Command+Q to exit the Assistant without completing Setup. Then click Shut down. When the new owner starts up the Mac, they can use their own information to complete Setup.
Other macOS Installation Options
When you install macOS from Recovery, you get the most recently installed version of macOS, with a few exceptions:
On an Intel-based Mac, if you use Shift+Option+Command+R during startup, you may be offered the macOS that came with your Mac or the closest version still available.
On an Intel-based Mac, if you use Option+Command+R during startup, you may be offered the latest macOS compatible with your Mac.
If you just erased your entire startup disk, you may be offered an earlier compatible version of macOS.
If the Mac logic board has just been replaced, you may be offered the latest macOS compatible with your Mac.