How did Aaron halt the plague that broke out after Korah's rebellion?

Answer: He offered incense among the people

Aaron ran into the assembly with his censer, offered incense, and stood between the living and the dead; the plague stopped.

“Moses said to Aaron, “Take your censer, place fire from the altar in it, and add incense. Go quickly to the congregation and make atonement for them, because wrath has come out from the LORD; the plague has begun.””— Numbers 16:46 (BSB)