This is the treatment for sour crop from the article I gave you a link to.
I advise against trying to make your chicken vomit because it may cause them to aspirate the sour liquid. Besides, it's very unpleasant for your hen, and she may hate you if you do it. (Curiously, most sour crop victims are hens.)
Nystatin is the best treatment for yeast infections, but it requires a prescription. Or you can try to locate medistatin which is for birds and doesn't require a prescription.
The easiest (and cheapest) to obtain yeast treatment, though, is miconazole, found on the women's hygiene shelf in the pharmacy. You can use either the suppositories or the vaginal cream. Measure a quarter inch of suppository or about half an inch of cream and give orally twice a day for seven days. Do not stop treatment before the full seven days are completed or the yeast may return.
You may see different strengths of miconazole, 2% or 4%, and wonder which to get. Either strength is fine. I prefer the 2% cream myself for economic reasons. The treatment with either strength is the same, twice and day for a full seven days.
Following treatment for sour crop, offer plenty of plain fresh water and boiled egg to get the crop operating again. I like to also give a probiotic or Greek yogurt to restore good microbes in crop and intestines.