Using insert php code snippet when processing a form on a website

I have the following html code to process a form:

<form id="finform" method="post" action=Cadiz.php>
…

<input class="submit_btn" type="submit" value="Calculate">
</form>

As can be seen from the forms code, when you click on the Submit button ( “Calculate”) runs the file Cadiz.php.

With Insert php code snippet, I created a snippet with the name of Cadiz and put in this snippet the code from Cadiz.php file.

Could you tell me please how I should correct the action=Cadiz.php code so that the form would use the snippet Cadiz?