To un-enroll contact from automation you need to make sure that you already have an ongoing automation workflow in your account. In automation page you can find the list of automation lists where you can find the “Recipients” just click on that it will take you to the Recipients view section. There you can find the “Un-enroll”  icon just click on that will take you to the pop-up page and just click on un-enroll. Which makes the contact to be un-enrolled from the automation list.