If a site has been shared with an external user, and you want to revoke that user’s access to the site, you can do so by removing that individual’s permissions for the site.
- Sign in to the Sharepoint portal.
- At the top of the page, click the app launcher , and then click Sites.
- Go to the site on which you want to withdraw an invitation.
- click Settings and then click Site Settings.
- Click People and groupsunder Users and Permissions.
- Select the group from the Quick Launchbar on the left which you want to remove users.
- Select the users you want to remove, click Actionsand then click Remove Users from Group.
- Click OK.