I resently bougth OEM CPU ryzen 5 3600.
Where can I check serial number from CPU?
Official guide (https://www.amd.com/en/support/kb/warranty-information/pib-authenticity ) says that you need the qr-code from the box.
The serial number is laser engraved on the CPU itself.
This a visual of what Black_Zion posted from AMD Warranty Request site: