It's probably an allergic type reaction to the monistat, rather than a chemical burn. It's not unusual for either men or women to get an allergic reaction to monistat used in the genital area, where the skin is fairly sensitive.
The main thing is to wash any remaining monistat cream off, to stop the reaction. Then moist soaks using epsom salts will be soothing and healing. You can do that about 3 times daily, perhaps soaking a wash cloth with the solution.
After the soaks, put a little 1% hydrocortisone cream on the reddened area.
You should notice improvement within a day or so, and I suspect that things will be back to normal within 3-4 days or so.
For future reference, men don't usually get a yeast infection from their wives, although they can get an allergic reaction from their wife's yeast. Yeast require moist warm areas, such as inside the vagina
, to thrive, and don't grow as well on exposed skin.
In case you get a reaction after intercourse with your wife, 1% hydrocortisone will usually resolve it. Plus try to keep the penis cool and dry as much as possible.