And again: Hearken, O ye house of Israel, all ye that are broken off and are driven out because of the wickedness of the pastors of my people; yea, all ye that are broken off, that are scattered abroad, who are of my people, O house of Israel. Listen, O isles, unto me, and hearken ye people from far; the Lord hath called me from the womb; from the bowels of my mother hath he made mention of my name.  1 Nephi 21:1

Mormons claims that 1 Nephi was written in 600 BC, during the time of the Old Testament and prophets such as Isaiah.

One time it uses the word "pastors" in 1 Nephi.  Would this be a word Nephi would know?

The Greek word appears one time in New Testament, never in the Old Testament.

So Christ himself gave the apostles, the prophets, the evangelists, the pastors and teachers...Ephesians 4:11

The Greek word is poimēn and it means a shepherd, a manager or director.  It was used as an overseer of the Christian church.

Since Nephi was Jewish, would he use the word "pastor"?  No.  There were no pastors in 600 BC.  There were only priests.  Priests carried out the temple sacrifices and were very different people.