Ad admob to sub list screen

Hello, I need help with ADMob. I have watched a couple of videos on how to add admob to your app inventor app. However, all the videos I have watched so far show how to add admob on the home screen of your app. My app is built in such a way that the home screen has a list of items and when each item is selected, it will lead you to a sub list of items. How do I get ads to show on the screen with the sub list of items since this screen is only visible when testing the app and not when building the app, therefore, I can’t drag and drop the admob extension onto the screen with the sublist of items? Your help will be much appreciated. Thanks.