Delete the unwanted parts and download the remaining segment as a new MP4 file.

How to split or cut videos and audio assets - Microsoft Support

Use the timeline slider to find the start and end points of the "piece" you want to create.

For a built-in option, open your video in the Windows Photos or Clipchamp app, move the seeker to your desired point, and use the Split (scissors icon) or Trim tool.

To create a "piece" or specific segment from a video file like , you can use various free tools and software to split, trim, or cut the original file into smaller parts. Tools for Creating Video Pieces