First test whether the current movie is recorded by two channels, that is, when playing the movie, double-click the small speaker in the lower right corner to pop up the adjustment window of the main volume, and move it left and right to see if the background sound and the original sound are separated. If the slider can't hear the original sound to a certain side, you can save the background music with most audio-visual processing software, and add your own dubbing, such as professional software such as drawing pictures or Premiere. Please refer to the help of the software for specific steps, and it is not clear here. The emphasis here is the processing principle.

Wish you success! ~~