Wanting to use the DOMEX Wordpress theme for a particular project, but I want to be able to utilize a custom header (via Elementor Theme Builder). However, and I could be mistaken, the Header for this theme appears to be hardcoded into the theme.
theme Author are best expert about their theme functionality and author is responsible to answer your technical query.
You can post a comment in theme Comments page to let the author know that you need their support. hope author will assist you and will reply your comment. Thanks