Navigate to your Desktop Dashboard

Click "App Settings" on the left-hand side

Click "App content"

Find the page that you wish to edit in your app, then click the pencil icon to view the buttons for that page:

Click the plus icon in the top right to add a new button

Select the type of button that you wish to add. In this example, we will add an "In-app link"

Type or paste the destination URL that you wish to set for this newly created button