Alma 4:20

And thus in the commencement of the ninth year of the reign of the Judges over the people of Nephi, Alma delivered up the judgment seat to Nephihah, and confined himself wholly to the high priesthood of the holy order of God, to the testimony of the word, according to the spirit of revelation and prophecy.

At the start of the ninth year that judges ruled over the people of Nephi, Alma gave the judge’s seat to Nephihah. He focused only on being the high priest of the holy order of God. He taught the word according to what the Spirit showed him and what prophets had said.

So at the start of the ninth year of the judges’ rule over the Nephites, Alma gave the judgment seat to Nephihah and devoted himself entirely to the high priesthood of God’s holy order—to bearing witness of the word through the Spirit of revelation and prophecy.