Do you have access to the old Folder HelpDesk Outlook folder? If yes, then just copy all the open tickets items from that folder to the new Folder HelpDesk Outlook folder.
If you had overwritten the existing Folder HelpDesk Outlook folder during the re-installation, then there is only one, rather troublesome, way to get back the Outlook ticket items: you have to manually set all the open tickets in the database to -1 flag, and then re-open them from the new Folder HelpDesk, via the Search closed tickets button, one by one.