If anyone comes across this need. This code works.

### place in functions.php file
if (isset( $_GET[‘show_header’] )) {
$show_header = $_GET[‘show_header’];
}

if ($show_header == ‘no’) {
add_filter(‘avia_header_class_filter’,’avia_hide_header’, 10, 1);
}
//###### Add new option for hiding header for mobile app display
function avia_hide_header($necessary) {
$necessary .= ‘ hide-the-header’;
return $necessary;
}

place in custom CSS area or file

html.hide-the-header #header {
visibility: hidden;
height: 0px;
}