In order to add modules to your custom coded email template, you will need to access the raw code of such template.
- Navigate to Content > Content Settings, and select Design Manager under Content Optimization System Tools.
- Locate the template in question under the Coded Template Files folder located on the left hand-side.
- Click on the Design Documentation link located at the top right. This document contains a list of all the different tokens and tags you can use to reference different modules within the email content editor such as Rich Text, Social Sharing, Main Email Body, CAN-SPAM, etc.
- Once you have added the necessary code, click on Publish Changes to fully save your recent edits.