You didn't mention the CMS the site was based on. So I got the URL from the video and looked at the source and see it is WordPress. The page you want to modify is the aMember signup page. Apparently somebody has added code to the aMember signup page to display the default WordPress sidebar. Assuming your WordPress theme has additional sidebars, you will need to change the code to display a different sidebar. If your WordPress theme doesn't have additional sidebars, you could see if a sidebar building plug-in is available for that theme or add code to the functions file to generate and register new sidebars.