Dumb question: how to update db after (re-)tagging?

I’ve freshly read in my source and noticed some tagging issues. I updated the tags (including new file date).
What’s the best way to read in new tags then?
Update db only reads files not in db, but how to go about after updating tags? Do I need to move retagged files to new path, clean db and update or is a “touch” of files sufficient?