In Schema App navigate to "Integration Methods" and then click on Javascript Integrations, followed by Google Tag Manager for the code that you need to copy. 

These instructions exist in the tool as well. 

  1. Create or Login to your Google Tag Manager account
  2. From Google Tag Manager, “Add New Tag”.
  3. Give the new tag a name, E.g. Schema App
  4. For the Product, choose “Custom HTML Tag”
  5. Tag Customization; Copy and paste the following javascript including the <script> tags into the HTML input area.

Sample Only:

<script src=""></script>

<script>schemaLoad("YourAccountID", "yourAPIKey");</script>

  1. Click On "Triggering", choose “All Pages”
  2. Go back to your dashboard and click on "Publish" in the top right corner of the page

This will setup the integration between Schema App and Google Tag Manager. Make sure to properly setup GTM with your website. You can find more information about this here