I was going to ask a question from the android app but the tag did not exist and I could not seem to add it.
Any advice on how to do this?
Short of telling the page to give you the full page instead of the mobile page, and then adding the new tag, there's not a way to do it.
The mobile pages, for whatever reason, don't support adding tags that haven't yet been created.
I suspect the app works similarly, as it is lacking many functions of the real site.