The below instructions will convey how to connect to GitHub.
Ensure you've read our article on integration prerequisites.
Head to the "integrations" tab visible at the top of the GAT login
Select GitHub (pictured below)
3. Add your GitHub personal access token and click "save".
3a. You can learn how to create a personal access token from this article from GitHub
You're all set!
4. You can get a great overview of exactly how you GitHub and Global App Testing can work over on the GitHub website.