How does the Custom Widget for Beacon Devices work?

I can’t seem to figure out how to get a custom icon for the Beacon Device.

I know there is a variable for the custom widget on the Beacon Device, but whatever I do, I can’t seem to get the arrow replaced with what is in the Widget. ( I know that I haven’t added anything in the Custom Widget variable, but it was just to display what I meant )

I also can’t seem to find any documentation regarding this…

Can anyone help me with this?