I suggest that you reach out to the form plugin author and ask if the plugin provides a filter for modifying the form action, and you could use that. You would add a function to your theme’s functions.php file. Without knowing the specific plugin, I can’t provide a detailed guide for this.
If the widget provides a template that you can override, you might be able to copy it into a child theme and then modify the form action URL. This won’t be affected by plugin updates.
If there’s no filter or no template available that you can, the only alternative would be using a custom JavaScript. You can use JavaScript to change the form’s action URL when the page loads. It would look something like this:
jQuery(document).ready(function($) {
$("form").attr("action", "new-action-url");
});
You can add this script to your site by enqueuing it in your theme’s functions.php file. Then replace “form” with a more specific selector if needed, and “new-action-url” with the URL you want.