3 Nephi 6:19

And now it was in the days of Lachoneus, the son of Lachoneus: for Lachoneus did fill the seat of his father, and did govern the people that year.

This happened in the days of Lachoneus, the son of Lachoneus. Lachoneus took his father’s place. He ruled the people that year.

This was during the time of Lachoneus the younger, who had taken his father’s position and governed the people that year.