How to recover a MacBook erased from Find My iPhone without a code?

I have an apple MacBook retina 12 inch and my little brother accidentally erased it from find my iPhone. I went on my laptop it asked for my pin which I then put my phone password and it work. And now it’s on a firmware page and I don’t know how to get off. Apparently I should have been give a Code when the Mac was erased but I wasn’t and I can’t find a code anywhere. I’ve gone on the app and on the website. I’ve tried putting In in recovery mode using a lot of different methods. I can’t go to the App Store because the Mac was a gift and I can’t contact the person for the recipe.

[Re-Titled by Moderator]

Original Title: My Mac was erased