How do I change the player on my Android TV Box?

[opengirl]

I just bought an Android TV Box (MX111). I was happily using it to play my MKV files and it suddenly stopped working. I had foolishly selected to "always" open files with a particular video player, but I want to switch players now, and see if it will work, but I can't find a way to switch video players... to undo that foolish "always" selection. Is there a way to do this that I have somehow missed? Thanks!

 

[Aquila]

Go into settings> apps > (find your app) to app info and there is a clear defaults option.