How to use tag mapper on existing and new books??

So I enabled tag mapper icons for the toolbar and added a few known tags that I want to normalize, ie: replace the tag if it matches pattern 'character A & character B' with tag 'character A/character B"

In the tag mapper (luggage tag) i see it says to apply to all my selected books but when I click 'ok', I don't see anything happen, no jobs and the tag hasn't been replace.

Am I missing a step somewhere? I know the rule works, testing it and I see the tag that it should replace in the tag browser..

if anyone can provide insight or help, it's very much appreciated!

Thanks