Nosebleeds are a symptom and can have a variety of causes. A cold washcloth on the back of the neck is a traditional first aid measure.
dr Annette Kerkhoff
If you have a nosebleed, sit up straight and let your head hang forward. Spit out blood from the throat. Pinch the nostrils together for a few minutes.
Place a cold, wrung-out washcloth or a cool pack wrapped in fabric on the back of your neck for 5 to 10 minutes – the cold causes the blood vessels in your nose to contract as a reflex. Caution: Severe or uncontrollable nosebleeds (more than 20 minutes in adults, more than 10 minutes in children) is an emergency.
This is what science says about home remedies for nosebleeds