Put the video with original subtitles on the first track (the top video track), then put a picture (you can choose any monochrome picture) on the second track, corresponding to the place where subtitles need to be covered in the first track, then adjust the size and position of the picture in the subtitle preview window, and then lengthen or shorten the playing time of the picture in the second track according to the length of subtitles. You can also adjust the transparency of the picture in the properties. The same method can continue to overwrite any other subtitles or pictures in the first track.

I hope the above will help you.