Mosiah 22:15

And now it came to pass when the Lamanites had found that the people of Limhi had departed out of the land by night, that they sent an army into the wilderness to pursue them;

When the Lamanites found out that Limhi’s people had left during the night, they sent an army into the wilderness. The army tried to catch them.

When the Lamanites realized that Limhi’s people had escaped during the night, they sent an army into the wilderness to chase them down.