Existing filename and tags

Hello All,
All the music I download already has a name that is usually ARTIST - TITLE but when I open MP3TAG on the files all the tags are blank. Is there an action that I can write that once selected could import the existing artist and filename into MP3TAG? There are times that the tags are correct for the way I want them to be and need very little massaging. I also have a quick question regarding tag preview when you use an action. I thought there was a tag preview window so after you removed a bunch of tags from the song you could check and see if it was done correctly, The software would let you preview the tags in a small popup box. At least that's what I remember. Thank you to everyone that can help answer my question, Stay safe.

Isn't this a very similar problem that has been discussed with you here: