Untitled

add_filter( 'get_search_form', function( $form ) {
	if ( is_admin() ) {
		return $form;
	}

	$new_text = "Change this Text";

	$form = str_replace( 'placeholder="Search …"', ( 'placeholder="' . esc_attr( $new_text ) . '"' ), $form );

	return $form;
} );