In order to change the layout of one of your existing bundles, go to the Bundles tab or Home Page inside the app, choose the bundle that you want to edit and click the edit icon on the far right.
You’ll be redirected to the first page of bundle creation and design. In order to change the layout, go to the next page: Select Display Structure.
You can preview how your bundle will look with each of the available layout options.
Check out this article for some ideas and recommendations for different types of displays based on the type of bundle you're looking to make.