code: protected void performRestoreOperation() throws CmsException {
  
          CmsUUID structureId = new CmsUUID(getSelectedItem().get(LIST_COLUMN_STRUCTURE_ID).toString());
          int version = Integer.parseInt(getSelectedItems().get(0).getId());
          if (version == CmsHistoryResourceHandler.PROJECT_OFFLINE_VERSION) {
              // it is not possible to restore the offline version
              return;
          }
          CmsResource res = getCms().readResource(structureId, CmsResourceFilter.IGNORE_EXPIRATION);
          checkLock(getCms().getSitePath(res));
          getCms().restoreResourceVersion(res.getStructureId(), version);
      }
docs: Restores a backed up resource version.<p>
  
  @throws CmsException if something goes wrong