How to Add thumbnails to YouTube Shorts

I go step by step to show how I add a custom thumbnail to YouTube Shorts using the mobile app. The only way to do this right now is by picking a frame from your video. So if I want a custom design, I just make it the first frame when I edit. Then I use the YouTube app to choose that frame as my thumbnail. You can't do this on desktop, it only works on mobile. I walk through the full process, from picking the video to selecting the thumbnail and uploading the Short. This helps me get the exact look I want for my Shorts.