I bought an unlocked refurbished Apple 8 phone from Walmart. I’m trying to open it up and it’s asking for a 6 digit passcode which I never had. What can I do?

You should return it to Walmart for your money back. That phone has someone elses account on it. Apple sells refurbished phones in the online store which you can access by clicking on iPhone on the black stripe at the top of each forum page.

As suggested above, return it. It was not properly prepared for sale.

If you purchased it from Walmart online, you need to be aware that much of the merchandise sold there is NOT actually sold by Walmart. They're getting almost as bad as Amazon when it comes to 3rd party sellers.