If you remotely locked your device using the Lock function in the '[Find My Device section on your account online, there is no Unlock function available, when you try to log into the device now, you should see an Administrator needs to log into the device, is that correct?
The only way to access that device now will be to reset Windows:
Click the power button on the login screen.
Press the Shift Key and click Restart
Your PC will boot into the Windows Recovery Environment
Go to Troubleshoot - Advanced Options - Reset this PC