Bought a preowned iPhone but found that it was network locked how do I know which carrier its locked to?

If it is running iOS 13 or 14 go to Settings->General->About->Carrier Lock and it should tell you what carrier it is locked to.

Or ask the person you bought it from.

If “Carrier” doesn’t tell you, use the Get Support link at the top of this page and see if Apple can tell you who it is locked to. It’s always possible that it is region locked and that the phone has never been used with any carrier. If that is the case return it for a refund; it is useless to you except in the country where it was originally sold.

So what if it says this? What would this mean? And how can it be fixed? (Photo attached)