Run automation on existing data

I just created an automation to check for a due date coming up in the next month and send an email reminder.

  1. How often will an automation run? It’s triggered to look for a due date in the next month, but how often will that be checked?
  2. If a notification is sent that Andrea is due for a test in the next month, will this automation continue sending emails during the next month until I change my due date?
  3. Is there a way to run this manually for all of my existing data?