How to upgrade os on a network unlocked phone

[Khafe]

Hello, I'm currently using a network unlocked AT&T Samsung galaxy note 8 in Nigeria(it wasn't bought in Nigeria obviously) . I have been unable to get OTA updates for my device because it's unlocked, that's why I decided to update the os (to android pie) manually by flashing a new firmware on my device. However, I'm a little confused about which of the firmwares to download, because the options for my country(Nigeria) and my current Nigerian carrier aren't available. I was wondering if I should just go for one with "Csc:CCT", "Region: USA" and "Carrier: Open". Or would that be a bad move?
Looking forward to your response, thanks