How can i get a four day old mallard ducking to imprint on me?

The mother and the other ducklings are in the nearest water source and she is not coming back to get it. You cannot imprint it, that happens in the first 24 hours and it does not know how to swim or find food. You can go to the nearest pond, lake or stream and see if there are mothers with similar sized ducklings there. Put the little guy near those ducks, they may just gather him into their own flock or he may die but that is natures way. At least 3/4 of all ducklings hatched do not make it through the summer.