Shut down the MacBook Air
Press and hold the power button until “Loading startup options” appears
Select Options, then click Continue
If prompted, choose an administrator account and enter the password
If you do not have the password, use Apple ID recovery if available
If the Mac uses Apple Silicon, use Recovery to erase the disk from Disk Utility
In Recovery, open Disk Utility
Select the internal Macintosh HD volume
Click Erase
Quit Disk Utility
Select Reinstall macOS
Follow the on-screen instructions
If Activation Lock appears, enter the Apple ID and password previously used on the Mac
If you cannot bypass Activation Lock, contact Apple Support with proof of purchase