So you have added a new device type to attributes, but no icon is appearing.
To add an icon, take the name you have applied for the new device type in attributes, lower case it, replace spaces with underscores and you have the filename.
Take your icon in SVG format (preferably scaled to 50 x 50 pixels) and store it at:
If you're on Linux, ensure the correct owner and permissions are set.
So if your new device type (added to attributes) is "Something IOT", your new filename would be something_iot.svg And if you're on Linux, it's permissions would be as below.
You should now see your shiny new icon, next time it's required.