Do you have a sick bird? Herbals and home remedies are not going to work to cure illness as well as medications that are made for that. Need to have certain meds on hand for the common things that pigeons may get sick with. That way you are ready if they are needed.
Other than that, just feeding clean healthy seed and clean water and good grit and calcium source will keep them healthy. Bird vitamins are good, ACV (apple cider vinegar) 1 Tablespoon to a gallon of water, a couple of times a week is good for their gut. Probiotics to keep their gut healthy is good.