Duck egg -mallard- shell is cracked but not the membrane - should I help?

It will need higher humidity so it doesn't get stuck in the shell. You should keep it moist with a fine warm water mist on the shell but not were it is cracked. When I helped a chick get out of it's shell I broke some tiny blood vessels that were attached to the inside of the shell and had to put flour on them to stop the bleeding. They can loose too much blood and die.