When the game launched under steam, at first accounts were split (you could start a new acc which you could only acces trough steam login & steam accs couldnt log in on the old ones)
However after a while they merged all acces points to the same pile & now it doesnt really matter which login system you use, both can acces all accounts.
to activate an old account you have to go to the kupai site (suggest opening it on google chrome, because it translates all the Chinese jibberish automatically) & use the "activate old account button.
if you dont succeed, hop on the NF discord & ask, players try to help eachother out in discord where possible.
kupai old account activation link;