Delete the Mac from your Apple ID device list
Sign out of iCloud on the Mac
Turn off Find My Mac
Remove the Mac from Bluetooth devices
Remove the Mac from Wi-Fi networks if needed
Erase the Mac using Disk Utility or macOS Recovery
Reinstall macOS if you want to keep using the Mac
Unpair the Mac from any linked devices
Remove the Mac from your trusted devices and accounts
Contact Apple Support if you need help removing activation lock