How do I set a default app, say for my music player?

[alchymmyst]

I want to set default apps, particularly for music on my LG V20. I was able to do it before on a defective phone, but in replacing it with the identical model, I can't find how to do it. Under Settings -> Apps -> App Info -> [any app], it has an item "Open by default", but all apps say "No defaults set", and I can't open that item to change it. It's making me crazy. Any idea how I can fix it?

 

[B. Diddy]

Welcome to Android Central! Moved from the Nougat forum to the V20 forum, because this kind of thing can be device-specific.

What app is currently opening by default for music files? Find that app in Settings>Apps, then tap Clear Default. Now try to open the music file again -- does it prompt you to select an app as a default? If your preferred app doesn't show up, then you can't use it as a default.