Itunes media folder not updating
I've bought a newer Mac Mini to use as an iTunes server. It's running OS 10.11.6 and iTunes 12.8.2.3
My iTunes media folder is on an external drive, as it was for my previous Mac Mini iTunes Server, and I've followed the steps to try and get iTunes to use this folder (advanced prefs > change iTunes media folder, and then File > Library > Organise Library > Consolidate Files etc.), but when I click OK nothing is happening.
The only songs I see in my Library are those I bought from the iTunes Store.
Short of re-importing thousands of songs, how do I get iTunes to show the music stored in this folder?
Mac mini, OS X 10.11