How did Moses help the seven daughters of the priest of Midian?

Answer: He watered their flock

When shepherds drove the daughters away from the troughs, Moses rose up to help them and watered their flock.

“Now the priest of Midian had seven daughters, and they came to draw water and fill the troughs to water their father’s flock. And when some shepherds came along and drove them away, Moses rose up to help them and watered their flock.”— Exodus 2:16-17 (BSB)