If you've added a video or GIF to a slide in PowerPoint, but now you want to remove it, you can do so easily:
Select the video or animated GIF on the slide.
Press the Delete key.
Note: If your video or animated GIF isn't removed by this action, the media has been inserted onto the slide master or associated layout. To delete a video or animated GIF file from a slide master, on the View tab, in the Master Views group, click Slide Master. In Master View, select the slide master or layout that contains the unwanted media.