There are both 7391 and 7391 2-in-1, and 7591 and 7591 2-in-1.   The 2-in-1s of both screen sizes use the same 10th generation CPUs -- and I can guarantee you that if a board was swapped, appearing with the incorrect screen size, the boards are identical. It is very common for the same board to be used in systems where the only real difference is the chassis/screen size.  
Early last year, my motherboard had to be replaced and since then, my computer show as 7591.   how can I change that???
Inspiron 7391 showing 7591 after motherboard change