The term "making sour" can be interpreted in a few different ways, so let's explore some antonyms for these different meanings.
If we're talking about making food sour, some antonyms might include sweetening, enriching, or enhancing. Instead of making something sour, you could add sugar, cream, or herbs/spices to balance out the flavor.
If we're talking about making someone sour (i.e. disgruntled), some antonyms might include pleasing, satisfying, or delighting. Instead of rubbing someone the wrong way, you could try to make them happy with a thoughtful gesture or kind words.
In general, antonyms for "making sour" might include improving, refining, or boosting - in other words, doing something to make a situation or experience better rather than worse.