Spotify has no button to join two accounts into one login. What you can do is merge the libraries: copy every playlist, liked song, album, artist and podcast from one account into the other, then keep using that one.
1. Decide which account to keep
Keep the account that has what can't be copied:
- Listening history, Wrapped and recommendations stay with the account that made them. Keep the one you listened to most.
- Premium, Family or Duo membership: keeping the subscribed account saves changing plans.
- Followers of your playlists and profile can't be moved.
- The login you want to use from now on (email, or Facebook, Google or Apple).
2. Copy everything into it
- Open soundmovr.com and make the free Spotify app it asks for (once, about two minutes).
- Connect the account you give up as "Move from" and the one you keep as "Move to".
- Press Read library, check what is ticked, and press Start moving.
Your own playlists are re-created with their names, descriptions, covers and song order. Playlists you follow are followed again. Liked Songs, albums, artists, podcasts and audiobooks are added. Anything the kept account already has is skipped, so nothing is doubled, and nothing is deleted on either account.
3. Close the old account (optional)
Once you've checked that everything arrived, you can close the old account from its account page on spotify.com. Cancel any subscription on it first. If you want to keep it as a backup, there is no harm in leaving it.
What can't be merged
- Listening history, Wrapped, and the taste profile behind Discover Weekly and Daily Mixes.
- Playlist folders, the people you follow, and followers of your playlists.
- The original "date added" of songs (the order is kept).