iTunes question

All the music I have on my Iphone is stored in a removable hard disk. Recently I unplugged it for a while, and when I went to back up my phone, suddenly iTunes was telling me it couldn’t find practically all of my music. I re-plugged in the disk, but it still wanted me to individually locate frickin 10,000+ songs. Can anyone tell me the fast fix to this? Also, how do I avoid it happening in the future?

I think I’ve had this problem (on a Mac), but it was so long ago I don’t remember what I did to handle it. There were steps like checking iTunes / Preferences / Advanced, and possibly changing or resetting the “iTunes Media folder” location.

Is this iTunes on a Mac or a Windows machine?

This thread may be helpful - it’s from 2013, but it seems to be similar to your issue:
https://discussions.apple.com/thread/5215489?tstart=0