@TeamYouTube I did a YouTube livestream and I got stuck with a thumbnail that I didn't select. I cannot delete it either I was in YouTube Studio. Please help me. Thanks.
Thanks for the detailed info. While we don't have an option to delete a thumbnail, we can go to the video editor, try uploading a custom thumbnail or select one which is offered to you. More info here: https://goo.gl/C54BHX . Hope this helps clarify.