To set the menu icon in the app, go to the "Design" in the Designer application.
Choose sub "Template". (It is at the bottom of the page)
In the window that opens, you can choose one of the standard set.
The right of the icon sets the list presented their image.
After selecting an appropriate set of icons to confirm your selection by pressing "Save".
You can also upload your own icon by going to the menu "Components" and select the menu item for which you want to download the icon and click on the icon badge.
As you can upload your own icon pop-up menu, or choose from ready.
En icon must be in PNG format, size - 96x96, color - black, no background, for example: