Adding people to your organization→
You can make anyone a member of your organization using their GitHub Enterprise username or email address.
Removing a member from your organization→
If members of your organization no longer require access to any repositories owned by the organization, you can remove them from the organization.
Reinstating a former member of your organization→
Organization owners can add former members to your organization, and choose whether to restore the person's former role, access permissions, forks, and settings.