It is so simple, just right-click on the video and select loop. MAC users, use 2 fingers to right-click.
Works great when you post photos to YouTube for end of end of year presentations. I use Movie Maker to make my slideshows, with just a couple of clicks. Then I save my movie to my computer and upload to YouTube. If you have a small number of photos, you can use YouTube Slideshow as well! This app takes some time for them to load, so this is why I jump into Movie Maker to do this if I have a lot of photos. Movie Maker is on your Windows 10 laptop. MAC folks, you can use Movie Maker.