Hi there,
Searches need to be output as form and requires some PHP – to use that in a Header Element you will need to create a shortcode – heres an example:
add_shortcode( 'searchform', function() {
ob_start();
?>
<form method="get" action="<?php echo esc_url( home_url( '/' ) ); ?>">
<input type="search" class="border-0" placeholder="Search" value="" name="s" title="Search for:">
<input type="image" src="add_you_search_image_url_here" alt="Submit" />
</form>
<?php
return ob_get_clean();
} );
Add that PHP snippet to your site to create the Shortcode: [searchform]
that you can add to your Header Element.
It will require some CSS to style