What was Jehu commanded to do?

Answer: Strike down the house of Ahab

The young prophet told Jehu to strike down the house of Ahab, to avenge the blood of the prophets shed by Jezebel.

“And you are to strike down the house of your master Ahab, so that I may avenge the blood of My servants the prophets and the blood of all the servants of the LORD shed by the hand of Jezebel.”— 2 Kings 9:7 (BSB)