If you have a My Best Buy® Credit Card, your rewards Member ID is often printed on the back of the physical card.
Since Citibank issues these cards, you can log in to the Citi Retail Services portal to view your account details and statements. best buy account number lookup
If you are at a Best Buy store and do not have your account number or card, a "Blue Shirt" associate can perform a lookup at the register: If you have a My Best Buy® Credit
The full 16-digit account number is located on the front of your My Best Buy® Credit Card, typically between the chip and your name. best buy account number lookup