On the left side in your app explorer navigate to ‘Navigation’ (with the house icon). 

it will open the navigation. In your navigation you can have multiple navigation profiles, for example ‘Responsive Web', ‘Phone Web’, etc.

Make sure in navigation profile your default home page is selected. Press the ‘Select’ button behind ‘Default home page’ and select your default home page. It can be a different page for the different navigation profiles.