What did King Manasseh do in his distress as a captive?

Answer: Humbled himself and prayed

Manasseh humbled himself and prayed; God heard him and brought him back to Jerusalem, and he knew that the LORD is God.

“And in his distress, Manasseh sought the favor of the LORD his God and earnestly humbled himself before the God of his fathers.”— 2 Chronicles 33:12 (BSB)