Add form with scripts in WP

I am trying to add code to my WPpost page, but I don't know how to add it.

I tried to add to the child theme, but it didn't work:

global $allowedposttags;
$allowedposttags['script'] = array(
 'type' => array(),
 'src' => array()
);

I have to add this source code to a classic WordPress page. How do I do that?