Change default icon of Toolbar plugin

I am trying to create a toolbar plugin. I need to change the default icon of the tool. How can I do it?

The Toolbar plugin sample uses multiple icons, some generated on the fly. I have an idea it will show answer best if you explore the sample deeper.

https://doc.developer.milestonesys.com/html/index.html?base=samples/pluginsamples/sctoolbarplugin/readme.html&tree=tree_1.html

https://github.com/milestonesys

Thank you