I was getting a root canal and dentist cut it on accident and now it hurts how can i help it heal faster?

What got cut?: Hard to tell from your question, maybe your cheek or gums were inadvertently cut during the root canal procedure? Warm salt water rinse 2x per day may help. One way to prevent such a problem is to do the root canal with a rubber dam in place, which holds the tongue and cheek out of the way and protects you (and from other harms). If this wasn't used, find a new dentist. Period.