Alma 50:9

And it came to pass that when Moroni had driven all the Lamanites out of the east wilderness, which was north of the lands of their own possessions, he caused that the inhabitants which were in the land of Zarahemla, and in the land round about, should go forth into the east wilderness, even to the borders, by the seashore, and possess the land.

When Moroni had pushed all the Lamanites out of the east wilderness north of their own land, he told the people from Zarahemla and the land around it to move into the east wilderness. They moved all the way to the borders by the seashore and lived there.

After Moroni cleared the Lamanites out of the eastern wilderness north of their territory, he had the people from Zarahemla and the surrounding areas move out to the eastern wilderness, all the way to the coast, and settle there.