There are two ways to deal with unwanted music on your Play Music application library depending on the source. The method will normally depend on whether or not your song is directly stored on your Galaxy S8 or Galaxy S8+ Plus.
For the music that is directly stored on your device, simply browse the song then hit the Menu icon. Select the “delete’’ command then hit the OK button to delete the song.
If you cant locate the delete command on the menu, the songs availability is only through Google Play Music. To remove the song, simply log in to the Google Play then view your library to try and locate the song. Then hit the Menu icon of the song and select delete command button to delete the song on Galaxy S8 and Galaxy S8+ Plus.
Add some new tunes afterwards as per your preference now that you’ve learnt how to clean up your music library.