The one-page designed of our theme is intended for one-page websites where place all your content on the homepage.
So you can only apply the one-page template to one page at a time.
You can create menu items to allow users to scroll down the page to their respective sections.
This will help you to set up the menu https://support.themely.com/knowledgebase/parallel-setup-navigation-menus/
Let me know if you have any further questions.