The Open Disc button is used to open video Blu-ray or DVD. Click the Open File button in the home interface to trigger the open-file dialog, find the MKV file that you want to watch and select it, click the Open button. Install the best MKV player on your PC and launch it.
Needless to say, it is the best option to watch your MKV video files on Windows 10/8/7 and Mac OS X.