My daughter's Macbook Air was accidentally erased from my iPhone 'Find My'. How can I revive it?

RyeHun Said:

"Thanks for your response. Does this mean I have to throw away the laptop? Is there a way to restore the Macbook in factory setting? It does not even start now. I don’t need to restore any data."

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You are welcome.

No. You shouldn't have to throw it out. Simply reinstall the macOS anew.

Reinstall the macOS Anew:

View my User Tip: How to Reinstall the macOS Anew - No TMB Prior to Upgrade - User Tip. Format the hard drive with the applicable macOS, on step D.

In Depth:

Pretty much, it is a matter of:

1. Erasing: and formatting your hard drive to APFS
2. Installing: [the applicable macOS] via a USB Bootable Installer
3. Restoring: info from a Time Machine Backup, using Migration Assistant

RyeHun Said:

"My daughter's Macbook Air was accidentally erased from my iPhone 'Find My'. How can I revive the Macbook? The Macbook wasn't stolen. My daughter still has it."

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Restore from a Backup:

Did you ever back up your Mac in the past? If so, then restore you Mac from the backup. If not, then you are stuck from here. So, take this as a learning experience knowing to always backup your device prior to installing an update. That way you can have something to restore it to, should you have issues (i.e. data loss).