If you forget to keep the original sound when changing the video, it may be because you are careless in operation or unfamiliar with related functions. In this case, you can try the following solutions:

1. Restore the original video: If you have a backup or copy of the original video, you can re-import the original video and replace it again, making sure to select the option to keep the original sound.

2. Use video editing software: If the original video cannot be restored, you can use professional video editing software, such as Adobe Premiere Pro and Final Cut Pro, to edit the replaced video. In the editing software, you can import the original video and the replaced video, and then extract the original sound from the original video and merge it with the replaced video.

3. Add audio tracks: If you can't use professional video editing software, you can also use some simple video editing tools, such as Windows Movie Maker and iMovie, to add additional audio tracks. On this track, you can import the original sound extracted from the original video and synchronize it with the replaced video, keeping the sound of the original video.

Extended content: In the process of video editing, it is very important to operate carefully and be familiar with the functions of the editing software. Before doing anything, it is recommended to be familiar with the editing tools used and read the relevant operation guides or tutorials carefully. In addition, it is also a wise practice to back up the original video to prevent unexpected operations from causing irreversible changes. The most important thing is to treat each step patiently and carefully to ensure the quality and effect of video editing.