Your Score widget displays the average score for all shops that the manager accessing the View has permission to see.
In the "Graph Types" setting, you will find a link to the IconoGraph example library. You can simply click on the IconoGraph type to get the URL to that icon. After you paste the URL to the input field, the widget will refresh and display the chosen image using colour saturation to visually represent the score.
"IconoGraph with Heat Mapping" is the same as IconoGraph except the original colours in the image are replaced with the heat map colour associated with the score.
If you don't fancy any of the icon templates in the IconoGraph library, you are free to enter a URL link to your own icon, set the Heat map option to the colour code that works for you, as well as ensure that the icon fills horizontally based on the score.
Remember to check a different help article detailing other settings of this widget.