How do I find the password to my Firmware Lock?

Have a look at > Set a firmware password on your Mac - Apple Support

If you forgot your firmware password

If you can't remember your firmware password, schedule an in-person service appointment with an Apple Store or Apple Authorized Service Provider. Bring your Mac to the appointment, and bring your original receipt or invoice as proof of purchase.

What if I don’t have my original proof of purchase

If you purchased the Mac directly from Apple or an Apple Authorized Retailer, then they should have a record of the purchase. If not, then you now own a giant paper weight that resembles a Mac.