locked out

From the link :  remotely locked using Find My

How do I unlock my Mac?

After you locate your Mac, you can unlock it with your passcode on iCloud.com. Make sure to use the passcode that you created when you locked it with Find My, not your device passcode.

Here's how to see the passcode that you used to lock your Mac:

1. Sign in to icloud.com/find. 
2. Select your Mac from the Devices menu. 
3. Select Unlock. After you follow the steps to verify your identity, you'll see the passcode that you need to unlock your Mac.

"Your Mac asks for a PIN code when it has been remotely locked using Find My. Enter the four-digit or six-digit passcode to continue."