Please see these posts for your problem, the first one worked very well for my website, since I had the same problem 🙂
https://ww.wp.xz.cn/support/topic/menu-and-top-menu-is-behind-slider-hero/
https://ww.wp.xz.cn/support/topic/menu-hidden-behind-site-origin-hero-slides/
Hope to have been helpful, bye!
