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In the upper-right corner of GitHub, click your profile picture, then click Organizations.
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Select an organization by clicking on it.
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Under your organization name, click Settings. If you cannot see the "Settings" tab, select the dropdown menu, then click Settings.

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In the "Third-party Access" section of the sidebar, click OAuth app policy.
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Next to the application you'd like to disable, click .

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Click Deny access.
Denying access to a previously approved OAuth app for your organization
If an organization no longer requires a previously authorized OAuth app, owners can remove the application's access to the organization's resources.