A few years back I had my chickens in a greenhouse for the winter, and I did not have enough ventilation. I had 1 chicken die from what appeared to be some sort of respiratory problem. Others were showing symptoms. I didn't have time or money to do much for tests, but I gave them oregano for their immune system, yogurt for some probiotics, and some apple cider vinegar with honey in their water for a few days for electrolytes and energy. I also fixed the ventilation. All recovered and returned to health.
The ventilation obviously helped, but several of them were severe enough I think they needed the extra boost from the other supplements.
Oregano, ACV, yogurt won't hurt anything... and they might help with healing.