Where can i put this html code and how

[trainwithavi@gmail.com]

Hi 
i want to insert a script code provided by an image host imgbb into my post reply and quick reply area 
where should i put the code 

The instructions says " Add it to your website

Copy and paste the plugin code into your website HTML code (preferably inside the head section). There are plenty options to make it fit better to your needs. "

the code to put in is :

Code:

<script async src="//www.imgride.com/sdk/pup.js" data-url="https://www.imgride.com/upload" data-palette="orange" data-auto-insert="bbcode-embed-full"></script>

Where exactly i want the upload option to appear is 
https://imgur.com/RqPqKs4
https://imgur.com/OJ1eroS
Please help with this basic query 
I already tried to put this code in new reply template like this 

Code:

<td class="trow2" valign="top"><strong>{$lang->your_message}</strong><br />{$smilieinserter}<!-- Imgur -->{$imgur_button}<!-- /Imgur -->[size=small][font=Monaco, Consolas, Courier, monospace]<script async src="//www.imgride.com/sdk/pup.js" data-url="https://www.imgride.com/upload" data-palette="orange" data-auto-insert="bbcode-embed-full"></script>[/font][/size]<br></td>

but its not working