The two stories are narrated in 2 Kings 21 and 2 Chronicles 33.  In the Kings account King Manasseh was completely opposite his righteous father, Hezekiah.  In fact, he was an unmitigated disaster for his idolatrous practices, which even included sacrificing his own son.  The incurred God’s wrath and subsequent judgment.  In the Chronicles account, Manasseh’s copious sins are also enumerated.  But in this account after he had been dragged off to Babylon in chains he humbled himself and implored God.  That eventuated in his return to Jerusalem and his fostering Israelite religious practices.  The two stories are impossible to harmonize.  The best we can do is to note that the characterizations suited differing purposes of the editors of Kings and Chronicles, respectively.