I don't have an idea about the ideal online platforms that can teach you to work with tissue foils, as I've gained my knowledge regarding this art form through a course on origami from Taro's Origami Studio. So I did not feel the need to opt for online learning. But as you've asked me for guidance, I did search for some videos and I found this link (https://www.youtube.com/watch?v=ssEuZVm5_7I) to be a reliable one with procedures similar to the one I'm currently following. You can follow this channel to learn the basics of using tissue foil for creating origami.