Soundiiz is supporting the import of Last.fm playlists to other streaming services by using the web URL !
For that, simply go to your playlist on Last.fm website then go to the playlist you want to export and once on the tracklist copy the web URL in your browser.
Then simply go back to Soundiiz, tab Playlists and use "Import playlist" button in top right of the interface and select "By URL". Then paste your URL and follow steps !