Is there any over-the-counter medications that can decrease blood ammonia in a cirrhosis patient and f so what?

Talk to your doctor. Elevated ammonia is a serious condition that should be treated with the advice of a doctor who knows you well. There are otc meds, but should be used only on doctors advice.
Ammonia. Medications that can cause loose stools can decrease ammonia levels so any stool softeners. But be careful to avoid liver toxic medications.