The phrase "put a damper on" means to spoil or ruin something. In order to convey the opposite meaning, we can use antonyms of the word "damper" and the phrase "put a lift on". Other synonyms for lifting someone's mood or enhancing the positive outcome of a situation could include "brighten up," "improve," "boost," "uplift," or "cheer." We can use these words in place of "put a damper on" to indicate a positive impact. For example, "Her unexpected visit really brightened up my day," or "Winning the championship game uplifted the team's spirits.