title: Airflow: Re-run DAG from beginning with new schedule
body: <p>Backstory: I was running an Airflow job on a daily schedule, with a <code>start_date</code> of July 1, 2019. The job gathered requested each day's data from a third party, then loaded that data into our database.</p>
  
  <p>After running the job successfully for several days, I realized that the third party data source only refreshed their data once a month. As such, I was simply downloading the same data every day. </p>
  
  <p>At that point, I changed the <code>start_date</code> to a year ago (to get previous months' info), and changed the DAG's schedule to run once a month.</p>
  
  <p>How do I (in the airflow UI) restart the DAG completely, such that it recognizes my new <code>start_date</code> and schedule, and runs a complete backfill as if the DAG is brand new?</p>
  
  <p>(I know this backfill can be requested via the command line. However, I don't have permissions for the command line interface and the admin is unreachable.)</p>