serial number on macbook

Perhaps through use of your Apple ID. Or macOS Recovery, etc.

The serial number of hardware won't work, that's in hardware.

• If you forgot your Mac login password - Apple Support

https://support.apple.com/en-us/HT202860

• How to Reset a Mac's Administrator Account Password | lifewire

https://www.lifewire.com/reset-mac-administrator-accounts-password-2259977

• 4 Ways to Reset a Lost Admin Password on Mac OS X - wikiHow

https://www.wikihow.com/Reset-a-Lost-Admin-Password-on-Mac-OS-X

• If you forgot your Apple ID password - Apple Support

https://support.apple.com/en-us/HT201487

• Recover Your Apple ID - Apple

https://iforgot.apple.com/password/verify/appleid

If you cannot use these, arrange to get help

from AASP or Apple store, online; genius, etc.

• Genius Bar Reservation and Apple Support Options - Apple

• Get Support - https://getsupport.apple.com/