if you still have corn put it in a bucket of water. that's how my ducks years ago learned to eat grains. they love to explore the bottom of a bucket of water.
I cannot read all the posts. my vet told me to give some (whole) barley to my ducks and geese when it is too cold. they don't like it much but I first give them barley and if hungry they eat. after barley I give them whole corn and wheat which they like. I have grass and they forage for snails...