Back up your data (Time Machine or other backup)
Sign out of iCloud, iMessage, and FaceTime
Restart the Mac
Shut down the Mac
Press and hold the power button until startup options appear
Select Options, then Continue
Choose Disk Utility
Select your startup disk (usually “Macintosh HD”)
Click Erase
Choose the format:
For Apple silicon: APFS
For Intel: APFS (or Mac OS Extended if required by your setup)
Click Erase, then quit Disk Utility
In the Recovery window, choose Reinstall macOS
Follow the on-screen prompts to reinstall macOS
After reinstall finishes, set up the Mac
If you’re selling or giving away the Mac, complete setup until the “Activation Lock” is cleared by removing your Apple ID (or erase again if needed)
If prompted for a firmware password or Apple ID, use the credentials associated with the Mac