You have become so bad through the years since I've been using Copytrans Manager. It messed up my playlist so badly, I'm done with you guys.
Hello!
Please, check this article to see how to delete music with CopyTrans Manager : https://www.copytrans.net/support/delete-music-from-iphone/
Check also this article from Apple if you can't delete a song: https://support.apple.com/en-us/HT204343
Lastly, reach out to the support team at copytrans@copytrans.net, we'll be glad to help you!
Best regards
CopyTrans Team