Remove Duplicate Tag Fields

I have a number of duplicated fields which appear after adding during a "TXT to TAG" import. I would like to remove the extraneous ones, such as "Comment" and "comments". I have a field called "Comments" I would like to retain. There are several others duplicated due to lower case tag names, which were in the sample Help file.

Note: These extra fields do not show up in the usual MP3 Tag display. They show up when using a program such as Audacity ("Edit | Metadata") where these fields can be removed, but only after importing the entire file, "Remove" (ing) the selected fields, and saving the entire audio file. There is no bulk tag editing (thus the need for MP3 Tag).

I doubt that.

Have you checked the dialogue "Extended tags" in MP3tag? Press Alt-T.
There you can see all the files that are present in the files.
You can remove duplicate fields there.
There is also an action to remove duplicate fields.