I found the parent category for Carlisle, Cumbria:
https://www.wikitree.com/wiki/Category:Cumbria
When you click on the red link for your category, you are taken to its edit page. In the edit box, you must enter the parent category's WikiTree ID, which is Category:Cumbria; enclose that text in double brackets to create the internal link, then save your edit.
After you refresh the page, you should see the names of any profiles that you have added to the Category:Carlisle, Cumbria category. When you go to those profiles, the link should be green.
If you have problems with this task, just post back and ask for additional assistance!