If you require a more unique icon to be displayed from the menu of your app rather than the icon designs available in the core you can upload your own custom icons.
Custom icons must be 171x128px in png format.
From the App element select Main Menu.
Select, Manage Custom Icons
The next screen will show Upload Icons and Existing Custom Icons (if you have not uploaded these fields will be blank).
To add an icon open a directory to where your custom icon is stored on your local machine, click on the icon then drag and drop the icon within the grey Drop icons here to upload.