How to recover serial number on Macbook?

Question

macOS

DD. Macbook Air 2012. I changed the hard drive and installed a fresh OS (Mojavi) from scratch, everything would be fine, but the serial number flew off: I

put the old disk with the old OS, but there is no more serial there, maybe I lost it somewhere before, I'm not sure here).
Google says about the method through the "Blank Board Serializer", but it doesn't load for me =(on the black screen, the text quickly jumps and starts to start the main system.
As I understand it, this happens when you change the motherboard, but I didn’t change that = /
I will be glad in any directions.

Answer 1

If information is not available even from "System Report...."
Try via terminal:
Two other obvious ways =) that you may have already used, but I'll write it anyway:
The serial number should be on the back of the MacBook and on the box . Of course, the number could be erased, and the box could be thrown away.