Issues flashing SM-N986U to SM-N981N firmware?

[catagris]

So the full series of events is I bought the phone from T-mobile, paid it off and unlocked it.
Moved it over to AT&T temporarily and there software/boot took over it.
Now I live in Korea full time and want to get software updates as well as remove the AT&T branding.

I thought maybe the best path forward was to flash KT's firmware for the same model phone but don't want to brick it.
Best path forward?

 

[alecxs]

I think these are different phones
https://www.gsmarena.com/compare.php3?idPhone1=10261&idPhone2=10325

 

[Romeo Nickolas]

You can only flash U1 and W on U firmware and vice versa.