These instructions exist in the tool as well.
- Create or Login to your Google Tag Manager account
- From Google Tag Manager, “Add New Tag”.
- Give the new tag a name, E.g. Schema App
- For the Product, choose “Custom HTML Tag”
<script> tags into the HTML input area.
- Click On "Triggering", choose “All Pages”
- 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.