To restore a Guru object, refer to Browsing, Importing, Exporting and Recovering Guru Objects document (take a look at the 'Recovering a Guru Object' section).
To find out which object class you need to select, refer to RI Guru Object Classes document.
For example, if you want to recover/restore a patch file:
You would select RiPatch for the ri.sys.ObjClass as shown below.
Then, select the patch which you want to recover and click the Revision History page at the bottom of the window.
You can see that there are 2 versions of this patch. Select the one which you want to recover, for example, the second one from the list, then right mouse button click and select the Make Last RevisionOf menu.
When done, you can see that there are now 3 versions of the selected patch.
Restart the Cassini System Software.