You can use the Windows 10 Photos app to rotate your video.
On Windows 10 you may use the Windows Photo Gallery or Photos App to view images. On Windows Photo Gallery you may right-click on the image after viewing it, and you get an option, “Rotate” which enables the image to rotate. You also have an option on the bottom right will rotation symbols to rotate the picture or video left or right.
If you are on the Photos App, you may use the Ctrl + R keys combination to rotate the image. You can also rotate the image manually by clicking on the round (rotating) arrow symbol.