Thanks for the response. Looking at the linked post again, I stumbled across the answer.
The linked post does not make it clear that you have to click on the "Tags" notebook title to the far left to get the editable list of tags to the right, as shown below. My cursor does not show up in this screen print, but the "Tags" notebook is highlighted since I clicked on it. Tags can be manipulated in the list on the right. Very unintuitive! I accidently clicked on the "Tags" notebook instead of the tag I wanted to delete, or I would never have found this.