We know, no one stated in the 1st Century words and phrases like Trinity, persons, three persons, triune godhead, and such in the Biblical century, so how about that second ?
Who did so, what was their name, what did they state that indicates , declares, even implies a Trinity or three persons?
Oneness do not see any, haven't found any and don't believe Trinitarians can either.
What century were the NT scriptures canonized?
4th century CE.
It was not until then that the whole Bible could be studied for the entire context of any and all doctrines and theology.
So your question is based on a premise as false as "Who in Eden knew of the global flood?" or "Did Noah know the law of Moses?"
Either you suffer from abysmal ignorance or you are attempting to prey upon those who do.