Video autoplay on mobile

I placed a video on autoplay with a loop in my header. It works perfectly fine on all devices with every browser, except apple mobile! There, the autoplay function is not working. Has someone any ideas how to fix this?

While my research for a solution I′ve found a function ?playsinline“, wich should solve this problem. But I don′t know where and how to add it to the HTML code of my WP-Theme Sydney. I really, really need this to work.

The page I need help with: [log in to see the link]