Change music library!

Hello, sueinspain.

Thanks for getting back to us here in Communities. First make sure you have a backup of your Music. Then you can follow these steps without using an external device: Move your iTunes library to another computer Basically copy all the music either into the same folder or create a new folder. Once that's done, follow the steps in the article to add the library: Switch libraries with the Music app or Apple TV app in macOS Catalina

Best regards.

Hello, sueinspain.

Thank you for using Apple Support Communities.

From what I understand is that you want to have only one music library instead of multiple ones. I'd like to help and I got an article to share that will help you with this by consolidating your music, check it out: Change where your music files are stored on Mac

"Consolidate your files in the Music folder

Depending on how you imported items into Music, some items in your library might be stored in different locations (for example, in another folder or on another storage device).

You can consolidate all the files in your library in the Music folder—for example, to make it easier to move your library to a new computer.

1. In the Music app  on your Mac, choose File > Library > Organize Library.
2. Select “Consolidate files.”
3. Files remain in their original locations, and copies are placed in the default folder".

Before making any changes, always make sure you have a backup of your music: Backup your Mac

Cheers!