How to change the Search Button label to a Search Icon
To change the Search Button label to a Search Icon (FontAwesome) add this codes to your theme functions.php file (at the end of the file)
add_filter( 'yith_wcas_submit_as_input', '__return_false' );
add_filter( 'yith_wcas_submit_label', 'my_yith_wcas_submit_label' );
function my_yith_wcas_submit_label( $label ) {
return '<i class="fa fa-search"></i>' . $label;
}