Add or remove shared folders and files in iCloud Drive on iCloud.com
After you share a folder, you can add folders and files or remove folders and files from it. All participants can access the folders and files you add but lose access to the ones you remove. Participants who are allowed to edit the shared files can also add and remove them.
Add a folder or file to a shared folder
In iCloud Drive on iCloud.com, drag the item to the shared folder.
If you place a file that’s already shared with others into a shared folder, only the participants of the shared folder can access it. Participants who previously had access to the file lose it (unless they have access to the shared folder). If you don’t own a shared file, you can’t move it into a shared folder.
Remove a folder or file from a shared folder
In iCloud Drive on iCloud.com, drag the item out of the shared folder.
All the participants of the shared folder lose access to the removed item.