Spotify features the option to submit songs that have not been published yet to their official curated playlists.
To do so, the artist, label or manager has to go to their Spotify for Artists account and select the track they wish to submit for playlists. The editorial team will consider the proposal and decide if the track is included or not and to what playlist. The final decision is always made by the professional Spotify team.
Spotify advises the users to make the request not less than 7 days before the release date as well as to introduce all the available information about the track.
More detailed information related to basic requirements can be found in the following entry, while all the data step-by-step can be checked in Spotify's Help Center.