Add custom symbol to a task

Hello, i have downloaded the camunda modeler exe from here: Releases · camunda/camunda-modeler (github.com)

Now I would like to add a custom symbol to a task like this little symbol on business rule tasks ( table ).
How can i achieve this?
I already read that i have to change the font class from bpmn.io of github here: bpmn-font/font-config.json at master · bpmn-io/bpmn-font · GitHub

But as i do have the .exe downloaded i cannot figure out where this is referenced and how i can add a custom svg.

Can you give me a hint on where i have to look?

Thanks a lot, greets Sebastian