Coral injuries can be quite traumatic.  The immediate first aid step is to wash the wound with clean fresh (not salt) water.  If available add a mild antiseptic in the water (like Betadine). Contrary to what most people teach, vinegar is NOT indicated for coral injuries.  Nor is urinating on the wound.  Using a dressing with antibiotic ointment and keeping the wound rested and elevated is sensible.  If any foreign object in wound, it needs to be removed.