customized video background not playing in mobile

Hello, I really love this theme and added an mp4 for the hero section background. All works well except it is not playing on mobile. I searched all night trying to fix this problem but it is just not working. I tried to add a quick script type="..." :  ... video.setAttribute("muted",true) , cannot reach the video's attribute. Apparently, I have to add video.play(), or make the users interact at least once to make it play, but not sure how to do it. Highly appreciated your help. Thank you.