Not knowing which version of Android your unit is running, changing the default player is done under an App Manager (or similar name). Find the player name in the list of Apps, click Set as Default, you should get an option to Clear Defaults. Then when the unit recognises a DVD you 'should' be prompted to select the App you want to 'Open with'. If that's how your unit responds and those steps make sense, you could try different Apps to see if one will work and play your DVD's. If none work, and your unit is able to connect to the internet, install VLC from the play store and try that as the default player.
Good luck!

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Neil

2016 X5 3.0D
2009 X3 3.0D
2005 X5 3.0 Diesel Sport (sold)
2007 320i (sold)