You cannot edit/update the content returned from iFrame untill it is on same domain. To access iFrame contents of different domain apply below solution.
This solution works same as iFrame. I have created a PHP script that can get all the contents from the other website, and most important part is you can easily apply your custom jQuery to that external content. Please refer to the following script that can get all the contents from the other website and then you can apply your cusom jQuery/JS as well. This content can be used anywhere, inside any element or any page.
<div id='myframe'>
<?php
/*
Use below function to display final HTML inside this div
*/
//Display Frame
echo displayFrame();
?>
</div>
<?php
/*
Function to display frame from another domain
*/
function displayFrame()
{
$webUrl = 'http://[external-web-domain.com]/';
//Get HTML from the URL
$content = file_get_contents($webUrl);
//Add custom JS to returned HTML content
$customJS = "
<script>
/* Here I am writing a sample jQuery to hide the navigation menu
You can write your own jQuery for this content
*/
//Hide Navigation bar
jQuery(\".navbar.navbar-default\").hide();
</script>";
//Append Custom JS with HTML
$html = $content . $customJS;
//Return customized HTML
return $html;
}