Unfortunately, Poppyz does not have a feature that allows the customization of the login form. However if you’re using a visual builder like Divi, you can just create a page and add the Divi Login module. This module is fully customizable. More info about it here.
Take note that by doing this you have to link your menu to the newly created page. WP login redirects will still use the one you set on Poppyz plugin settings. Do not use this page for your custom login, or unselect it from Poppyz settings.