Happy to help! 
I'd take it out of the cup tomorrow (it may even flop out of there on it's own when it gets stronger). The duckling is still inside the egg in the cup right now, right? By tomorrow the navel should definitely be closed up and duckling hopefully more active and moving around.

I'd take it out of the cup tomorrow (it may even flop out of there on it's own when it gets stronger). The duckling is still inside the egg in the cup right now, right? By tomorrow the navel should definitely be closed up and duckling hopefully more active and moving around.
Don't disrupt this last guy that's hatching again just to clean cup duck's navel though. If you can wait until the last one is out that would be much better for all. Then you don't have to worry about losing humidity. They don't need the humidity any more once they are all out.