@joeleger This would remove all the selected tags from all your selected tracks. Not only the ones with PMEDIA inside a specific tag.
You need to find the tracks with the tag containing PMEDIA first. Then you can use your steps.
Otherwise you delete content from tags that you want to keep (content that could be something else then PMEDIA).
As @ohrenkino wrote more then 10 years ago in the above linked thread, please use a Filter (F3) first:
and enter PMEDIA to show only tracks with PMEDIA somewhere in your tags.