Как при селекте, менялись значения в другой форме?

<?php

$parsingGreec = new stdClass;
foreach ((array) get_post_meta('33688') as $k => $v) {
    $parsingGreec->$k = $v[0];
}
?>

<?php
 $args = array(
    'numberposts' => 0,
    'post_type'   => 'parsing'
);
$catPosts = get_posts($args);

echo '<form method="POST">';
echo '<select>';
foreach ($catPosts as $singlePost) {
    echo '<option>'.$singlePost->post_title. '' .get_post_meta($catPosts).'</option>';
};
echo '</select>';
echo '';
echo '</form>';
print_r($catPosts);
?>

<div class="flex_grid">
<form method="POST" id="form_post">

<label for="lft_after_before_field">C какого числа: </label>
<input type="text" id= "lft_after_field" name="startdata" value="<?echo $parsingGreec->month_after_value_key ?>" size="25" />
<label for="lft_after_before_field">По какое число: </label>
<input type="text" id= "lft_before_field" name="enddata" value="<?echo $parsingGreec->month_before_value_key ?>" size="25" />
<label for="lft_after_before_field">Количество ночей: </label>
<input type="text" id= "lft_night_field" name="night" value="<?echo $parsingGreec->parsing_night_key ?>" size="25" />
<button type="submit" value="parsing">Спарсить</button>
<?php print_r($_POST['lft_before_field']); ?>
</form>