How to bypass firmware lock on Mac after mistakenly pressing 'Erase device'?

How do I get past the firmware lock?

I just bought a new macbook and made a stupid mistake when trying to remove my old macbook from Find My. I pressed Erase device instead of Remove. Now I can't access my old macbook to restore factory settings. I just get the padlock and I have no idea what it is expecting. I have tried my Apple ID but no joy. Any help greatly appreciated

[Re-Titled by Moderator]

Original Title: Firmware Lock?