Add or remove shared files and folders in iCloud Drive on iCloud.com
After you share a folder, you can add files and folders to it or remove files and folders from it. All participants can access the files and folders 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 file or folder to a shared folder
In iCloud Drive on iCloud.com, do one of the following:
Drag the item to the shared folder.
Select the item, click
in the top right-hand corner, click Move to Folder, select a shared folder, then click Move.
If you place a file that is 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 their access (unless they also have access to the shared folder). If you do not own a shared file, you cannot move it into a shared folder.