Picard isn’t really the ideal tool for deleting duplicates, but you can use a pretty basic workaround.
Tag all of your music with Picard, and Picard will name duplicates of a song with a number on the end, eg:
01 Coffins.flac
01 Coffins (1).flac
Then you can search your whole music folder for ‘(1)’ (and (2) etc if necessary), and delete them all at once. It’s up to you to check that these are really the files you want to delete!
If you wanted something more specific or anything else, let us know!