It’s probably because the code is already in your child theme’s functions.php file by default. Just search for the code in your functions file, it should look like this –
// Customize search form input box text
add_filter( 'genesis_search_text', 'custom_search_text' );
function custom_search_text($text) {
return esc_attr( 'Search...' );
}
You can change the Search...
part to whatever you need and then it should work fine.