If you have unwanted organizations showing in the “Switch Organization” drop-down box in the upper left-hand side of the UI, you can revoke access from CircleCI in the GitHub project’s settings. This article is currently only applied to GitHub.
User accounts are also considered organizations, and so you may see them stuck in your organization list if you've contributed to a repository before. Follow these instructions to remove yourself as a collaborator from other repositories.
Note: You must be an Administrator of the Organization to make these changes
Revoking Access on GitHub
Navigate to your organization's Third-party access Settings page:
Click the "Setup application access restrictions" button(If you have a different page, applications may already be setup. Skip to step 4)
Click the "Restrict third-party application access" button
Click the pencil icon next to CircleCI
Click the "Deny Access" button
Now your CircleCI will no longer have access to your organization, and will not display it within the CircleCI organization drop-down. You can provide application access to CircleCI again at any time.