Grit is an important item to include in treatment of impacted crop. It won't hurt for sour crop, but it isn't going to have a direct effect.
Miconazole is an anti-fungal med and very effective, low cost, easily available without a prescription in most places, especially the USA.
People get confused about feeding during crop treatment. If the issue is impacted crop where the crop is already stuffed with solid food and other organic matter, putting more food into a chicken isn't going to help matters. Giving food to a chicken with sour crop is okay as long as it's low in carbs as sugars feed Candida.
I've found that a chicken with impacted crop will usually drink a lot of water and turn down food, while a chicken with sour crop will eat food, but turn down water. This is generally. Individual mileage may vary.
If in doubt as to whether or not to feed a chicken with a crop disorder, offer foods such as dry feed, boiled egg, or yogurt, make water available, and let the chicken decide if and when she wants to eat and drink.