I wanted to store my itunes library on an external harddrive however midway through doing this iTunes updated to being seperate apps, music, tv etc and now I can't get it to work

I wanted to store my iTunes library on an external harddrive when i changed to my new macbook however midway through doing this iTunes updated to being seperate apps, music, tv etc and so now when I go to do the old way of connecting my itunes library (opening the new music app while pressing shift, choose library) my iTunes folder on my external hard drive it won't let me select it. Does anyone have any idea how to get this to work with the new app set up?