How to remove an audio track from an mkv ?

You can use final cut pro x or iMovie on Mac OS, or Camtasia Studio or Adobe Premiere Pro or DaVinci Resolve on Windows, or DaVinci Resolve or Blender or Kdenlive or ShotCut on Any Linux distro. But I prefer command line tools.

1. Install mkvtoolsnix or use HomeBrew to install it : brew install --with-qt5 mkvtoolnix.
2. Use mkvinfo to get the audio track IDs that you want. command like this mkvinfo *.mkv.

Note that the audio track IDs are not the track numbers. Check the man page of mkvmerge or mkvinfo for more details.

3. Use mkvmerge to create a copy of the mkv with ONLY the desired tracks using --audio-tracks. The whole command be like that : mkvmerge -o out.mkv -a 2 orig.mkv.