You will need the email template source code to input this into your email template in the CMS.
First, create a new template in the CMS and press Save As New.
Then you will need to send the email template to yourself and then open it up in your browser.
When the email is open in the browser, right-click and select View Page Source Code.
This will open up code in a new tab.
Then in here, you will need to copy all of the code.
To paste this into the template, go into Content 1 and click the Source button and then paste the code into here and press Source again.
This will show your email in the template.
You can then make any changes that you need to in here and then press save.