The automation tool that should be used to accomplish this is creating an automation rule to register prospects based on the form submission. An automation rule is a rule that runs continuously in the background and matches prospects based on the criteria you set. You can use an automation rule to perform actions on the matched prospects, such as registering them for a webinar. For example, you can create an automation rule that matches prospects who have submitted a specific form, and then use the action Register for Webinar to register them for the webinar that is integrated with Marketing Cloud Account Engagement.