What should the hen do?

Prepare the nest!

If there are eggs in the nest, let it hatch by itself. You just need to prepare food and water regularly. Hens usually have to hold their nests for more than 20 days. Prepare it every two or three days (the details are not clear) and put it by the nest. If there are no eggs, go to the old man and ask him to pick some eggs for you.