Removing yourself from a collaborator's repository
If you no longer want to be a collaborator on someone else's repository, you can remove yourself.
If you're using GitHub Free, you can add unlimited collaborators on public repositories, and up to three collaborators on private repositories owned by your personal account. To add more than three other people as repository collaborators, upgrade to GitHub Pro.
In the upper-right corner of any page, click your profile photo, then click Settings.
In the left sidebar, click Repositories.
Next to the repository you want to leave, click Leave.
Read the warning carefully, then click "I understand, leave this repository."