As an organization owner or project board admin, you can remove an outside collaborator's access to a project board.
In the top right corner of GitHub, click your profile photo, then click Your profile.
On the left side of your profile page, under "Organizations", click the icon for your organization.
Under your organization name, click Projects.
In the projects list, click the name of the project board.
On the top-right side of the project board, click Menu.
Click , then click Settings.
In the left sidebar, click Collaborators.
Next to the collaborator you want to remove, click X.