Flasker on "Hello i need some help in Woocommerce"

Hello guys i´m from Azores and i need some help..

I programming in php but a have one problem to finish one job.
I want put this code in review-order.php

<select onChange="this.form.submit()" name="insurance_select">
  <option value="1" >YES</option>
  <option value="2" >Não</option>
</select>
</form>
<?php
if(!empty($_POST['insurance_select'])){
$_SESSION['seguro'] = $_POST['insurance_select'];
}
?>

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But the post don´t work. I don´t understand this.