how to change preview of mp3 file?

How do I change the preview of an mp3 file?

I have tried two things.

1) right click the mp3 file on my desktop. hit "get info". look fo options to change the preview under the preview section (turns out there are none)

2) open the mp3 file in the music app. change the album artwork. drag and drop the file back onto my desktop. Sadly, the album artwork doesn't seem to transfer with the file.

I am trying to add local files to my Spotify but if the preview isn't change (even if the album artwork is in the music app) then there is no album artwork on Spotify

Example: