What did Hezekiah do when he heard the Assyrian threats against Jerusalem?

Answer: Tore his clothes, wore sackcloth

Hezekiah tore his clothes, put on sackcloth, went into the house of the LORD and sent for the prophet Isaiah.

“On hearing this report, King Hezekiah tore his clothes, put on sackcloth, and entered the house of the LORD. And he sent Eliakim the palace administrator, Shebna the scribe, and the leading priests, all wearing sackcloth, to the prophet Isaiah son of Amoz”— 2 Kings 19:1-2 (BSB)