Extract the ZIP file and run miflash_unlock.exe as an administrator.
Go to Settings > About Phone and tap "MIUI Version" seven times to enable Developer Options. Then, go to Additional Settings > Developer Options > Mi Unlock Status and tap "Add account and device." miflashunlocken7672743
In the same Developer Options menu, toggle on USB Debugging and OEM Unlocking . Extract the ZIP file and run miflash_unlock