how to update itunes library location

Greetings marcfromcalgary, 

We understand that you’re looking to redirect your Music/iTunes library on your iMac. 

You’ll find this article has information on that, and using the drop-down at the top left you can change from macOS Big Sur to macOS Catalina for steps. Change where your music files are stored on Mac

In iTunes on Mac, that preference should be in iTunes > Preferences > Advanced and you can point it to the iTunes Media folder location. 

Thanks.

marcfromcalgary,

This is something that changed in macOS Catalina with the move from iTunes to the Music app. You mentioned using a newer Mac as well. By default in macOS Catalina and macOS Big Sur your music is stored in Home/Music/

Does that information help you locate the files via your newer Mac? If you right click on a song and choose to Get Info show you a location that you can point your older iMac to?