Unfortunately, you cannot reset the count. The default label is simply the current number of nodes. E.g. if you create three nodes "1", "2", "3", then delete node "2", then create another new node, that last node will be labeled "3" and you will end up with node "1", "3", "3". The only option available is to turn off default labels altogether (to do that, go to "File" -> "Preferences", tab "Editor", option "Create Default Label for New Nodes").