Office 365 (OneDrive for Business and SharePoint) - Stop Sharing a File or Folder
You can stop sharing an item, or change the permissions others have to it, if you're the owner of the item or have edit permissions.
1. Navigate to OneDrive for Business and SharePoint by logging into portal.office.com and selecting "OneDrive" icon
2. Select the file or folder that you want to stop sharing.
3. Click on the "information" icon in the top right corner of the screen.
4. Click on "Manage Access" and then "Advanced"
5. Now there are a list of users that have access to the file or folder that you manage.
a. Click on the "Manage Links" and then "Shared with" to manage which user's have access to the folder or file, as well as their level of access.
b. Click on the permission level drop down arrow, and select "Stop Sharing" to disable the user's access to the file or folder.
Please see this article on Microsoft's support site regarding how to stop sharing files or folders in OneDrive for Business or SharePoint sites.