First of all, in most video websites, you can find the option of "viewing history" or "watching recently" to view the recently watched videos. Secondly, if you watch videos through a browser, you can look for related videos in the history of the browser. Third, if you remember part of the content or title of the video, you can use the search engine to search for related keywords, and you may find the video you have seen. Finally, some video playback software also provides viewing history, such as Youku video.