What should I do with a music tape I borrowed from someone who traveled to Italy and whom I cannot contact, knowing that Allah has guided me and I have stopped listening to music?

The best method is to erase the forbidden music on the tape and replace it with a beneficial lecture about the ruling on music, then send it back to its owner, hoping that Allah guides him. If it's not possible to send it, then give it away as charity on his behalf. If the owner requests it, replace it with a similar tape that does not contain music.