Make sure you're signed in to your YouTube account. Click on the “History” tab. Then YouTube will show you all the videos you’ve recently watched in the timeline on the “History” page.

On Pc: Sidebar > History

All you need to do is click on the “X” symbol of each video if you are using a PC. Or tap the three dots appearing in each video and click on the “Remove from watch history” option.

On Mobile: Library > History

To clear recently watched videos using your mobile phone, Simply click on the three dots of any long-form video or short video and Select “Remove from watch history”. Also, you can simply find the delete button by swiping the video left for long videos on mobile. But it’s most probably available for long videos on mobile.

Unfortunately, the “X” symbol to clear watched videos on the YouTube mobile app isn’t available. Hope it will be added to the mobile app as well in the future by YouTube developers as it’s an easy option to smash a watched video in only one click.