If you have run a mass tag and now want to undo the mass tag you ran, the first step is to run a search for the tag just applied by you. For example, if you mass tagged a group of documents with the tag "Hot", you will run a search for tag("Hot") and tag(by [your user name]).
Just like you chose the "Tag" option to run the mass tag in the first place, you will select this same "Tag" option to also undo the mass tag. This "Tag" option is found on the top right of the 'Review' page, below the Search Bar but above the results.
After you click on this "Tag" option you will insert the tag "Hot" you just applied in your Mass Tag into the "Remove" section and then click on the blue "Tag" button on the bottom right corner.
Once you have started your removal of the mass tag, the bell icon on the very top right corner of the 'Review' page will update you on the progress of the removal of the tag "Hot". It will show the number 1 by the bell. If you click on the bell and the removal has completed you will see a message such as this:
If you are not sure if the tag was removed or if you have any questions don't hesitate to contact DISCO support at firstname.lastname@example.org.