Reordering metadata in Mp3Tag (Artist-Title format?)

I have about 500 MP3 files that all follow this specific pattern: song title - artist and I am trying to rename them to artist - song title
I went ahead and installed Mp3Tag, and I thought I was following the instructions perfectly—really, I did—by doing this:

I selected my tracks and ran the convert/tag-filename command. In the format string field, I entered: %artist% - %title% but absolutely nothing happened—no renaming at all.
I even tried switching the string to %title% - %artist% just to see if that would trigger anything, but still, no luck.
Does anyone happen to know what I might be doing wrong here? Or perhaps there is another program—or maybe just a different method entirely—that could help me get this done?

First, you gotta pull the tags straight from the file names (hit Menu Convert > Filename - Tag)
%title% - %artist%

Once that's done, just rename the actual files using those tags (go to Menu Convert > Tag - Filename)
%artist% - %title%

That’s absolutely spot on!
Thanks