The phrase "make hash of" implies that something has been ruined or turned into a mess. Antonyms for this phrase, therefore, would be words that indicate the opposite - things that have been fixed or made better. One antonym could be "improve," indicating that something has been made better or corrected. Another antonym could be "restore," indicating that something that was damaged has been returned to its original state. "Mend," "repair," and "fix" are also antonyms, as they all suggest the act of making something right that was previously wrong or broken. Ultimately, the antonyms for "make hash of" all revolve around the idea of taking something that was broken or ruined, and making it right again.