If you accidentally deleted a folder or file, you can restore the folder or file again so it will be available again.
Here's a little guide:
1. You will have to go to your web-client and login.
2. Select the shared folder which contains the deleted items.
3. Select "Deleted Files" at the top.
4. Now you will see all the folders/files which has been deleted in this folder.
5. Hold your mouse over the Trashbin icon, and select restore.
6. Now the file/folder will be accessible again.
Here's a short how-to video:
See also our solution "Synchronize your files for offline access"