Collapse / Expand Click Groups

Hi all together,

https://datatables.net/extensions/rowgroup/examples/initialisation/customRow.html

I like to have a possibility to click on the group name like "Averages for Edinburgh" and the group should expand/collapse. Per default when loading the site, the group should be collapsed.

For doing that, I also found this thread here, where redwall was able to embed such a function for his DataTable:
https://datatables.net/forums/discussion/comment/61474/#Comment_61474

But my Javascript skills are less than available

Would someone of you be so kind and help me out here? How can I reach the above described functionality on the basic example of "Custom row rendering / aggregates"?

Thank you for your help!!