Soundiiz supports importing BNDCMPR playlists to other streaming services by using the Share/playlist URL in your browser.
To do so, go to your playlist on the BNDCMPR (Bandcamper) web interface and copy the URL in the address bar.
The URL should like for example: https://bndcmpr.co/ec29f13c
Then simply go back to Soundiiz, tab Playlists, use the "Import playlist" button at the top right of the interface, and select "By URL." Then paste your URL and follow the steps!