In order for Google Tag Manager & Groupdesk to work together, you will have to provide the GTM ID to your Groupdesk contact. Once this is set up, you can create and edit tags yourself.
We recommend you create a Google Tag Manager container just for your Groupdesk web projects. (ie: You'll have a different key for your main website and your Groupdesk Traveler Interface subdomain)
How to access your Google Tag Manager: