A CRON task is something you configure within your host. You need to have it do a wget or curl call to the auto action URL if you're wanting to execute that auto action on a schedule. Note if your auto action relies on having a user object then the CRON task will be running the auto action as if they're a guest user (not logged in) so you need to take this into consideration. I don't recommend digging deeper into CB Auto Actions advanced usage cases like this until you first become more familiar with CRON. Below are example CRON task structures.
www.joomlapolis.com/forum/277-cb-paid-subscriptions-support/237481-cron-job#297853
As for how to setup CRON you'll need to contact your host as it depends a lot on their hosting interface as they could have a guided setup for configuring CRON tasks.