When you've configured and published your alert, link to the alert from one of your main PageBuilder pages. Remember to publish the alert before you provide the link!
Note: Users occasionally create a "PageBuilder-hosted Action Alert" by pasting the webform code from the Take Action page directly into a PageBuilder page (using the HTML Content component) and then customizing the code themselves. This method is not supported by Luminate Online. However, if you do this, make sure you host each alert on its own page and adhere to the subject and new_msg input element naming convention (which appends the Alert ID to the input names).