If you have v3, the most recent release of Tagger, it's on City Hall > Enable Sim Tags > True. If you still have v2, the older version, I believe it's only on in-game computers.

^- If that doesn't work, try making filter as written in here: Tagger FAQ Filter, as for the criteria, choose "Non Active", then enable it in tagger and they all should show up.

I had v2 of tagger installed, didn't know a v3 was out. So I downloaded and installed v3 enabled it and all my tags are back ! Thank you !