Okay. So you will have to create a child theme, if you have not already, then copy the header.php file, locate the code section where you want to place the shortcode. That is different for every theme, so I can’t tell where exactly. The theme developer will know, but they may not have support to do so.
If you have no experience with editing the theme files, you may need to ask a developer to help, as making direct changes to the theme files can be difficult.