I want to allow html tags on customer note in view-order page

I got temporary solution..
In /wp-content/wp-includes/kses.php file, I added

'iframe' => array(
	'title' => true,
	'line' => true,
	'width' => true,
	'height' => true,
	'frameborder' => true,
	'src' => true,
	'webkitallowfullscreen' => true,
	'mozallowfullscreen' => true,
	'allowfullscreen' => true,
			),

Is there any way put this function in theme’s function.php instead of doing this in wp core file?

You can find such code snippets / tutorials on allowing more tags with in a specific area or site-wide usage by adding some hooks to your theme’s functions.php .

/* You can add other HTML tags (and attributes) to your allowed html tags list

function my_allowed_html_tags() {
  define('CUSTOM_TAGS', true);
  global $allowedtags;

  $allowedtags = array(
      'a' => array(
           'href' => array (),
           'title' => array ()),
      'blockquote' => array(
      'cite' => array ()),
      'cite' => array (),
      'code' => array(),
      'em' => array(),
      'strong' => array(),
      // <p> and <pre> were not allowed by default in kses.php file; so here we add them.
      'pre' => array(),
      'p' => array()
      // and here is the <iframe> tag you mentioned
      'iframe' => array(
	'title' => true,
	'line' => true,
	'width' => true,
	'height' => true,
	'frameborder' => true,
	'src' => true,
	'webkitallowfullscreen' => true,
	'mozallowfullscreen' => true,
	'allowfullscreen' => true,
			),
  );
}
//Hook this new function to the specific action (init).
add_action('init', 'my_allowed_html_tags', 10);

Thanks for replying, ManusH.
Unfortunately, it didn’t work for me.

I also tried

function my_allowed_html_tags() {
  define('CUSTOM_TAGS', true);
  global $allowedtags;

  $allowedtags = array(
      'pre' => array(),
      'p' => array(),
      'iframe' => array(
	'title' => array(),
	'line' => array(),
	'width' => array(),
	'height' => array(),
	'frameborder' => array(),
	'src' => array(),
	'webkitallowfullscreen' => array(),
	'mozallowfullscreen' => array(),
	'allowfullscreen' => array(),
			),
  );
}

add_action('init', 'my_allowed_html_tags', 10);

and instead of ‘init’, tried ‘comment_content’ and ‘comment_post’ and ‘$note’.
But shouldn’t ‘init’ be working everywhere?
Anyway, none of them worked..

This is the line that makes customer note work, I guess.
woocommerce/includes/admin/meta-box/class-wc-meta-box-order-notes.php

<?php echo wpautop( wptexturize( wp_kses_post( $note->comment_content ) ) ); ?>