Clear textarea with default value after submit

I’m using wpcf7_form_tag action hook to add a text inside textarea field if page has a specific condition:

add_action( 'wpcf7_form_tag', function($scanned_tag, $this_exec) {
    $product_id = get_query_var('product_id', false);

    if ($product_id) {
        if($scanned_tag['basetype'] == 'textarea') {
            $text = 'sample text';
            $scanned_tag['values'][0] = $text;
        }
    }

    return $scanned_tag;
}, 10, 2);

The problem is that after sending the message, the textarea field is not cleared. The text is still there.