Unless they are acting sick or they keep laying soft shelled eggs, I don't think you will need to give them anything. Chickens can lay weird eggs for many reasons, some common reasons include:
Injury. Landing wrong when they fly off the roost, can cause hens to lay weird eggs.
stress can cause hens to lay soft shelled eggs sometimes
High egg production. When a hen reaches her top rate of egg production sometimes her system can't keep up, resulting in soft eggs.
Age. I don't think this is your problem but it helps to know all the possible reasons

Weather. hens can lay soft eggs because warm weather. Again I don't think this is your problem but it may help you later
Lack of calcium. The shell is made of calcium so naturally if a hen doesn't get enough then the shell gets soft.
These are all causes I have encountered but here are some diseases I don't know much about that cause soft eggs:
Infectious Bronchitis -common
Avian Influenza -rare
Newcastle disease -rare
Ornithobacteriosis (big word huh?) -rare
I don't know much about these diseases but I have a very reliable book about chicken health that lists them as conditions that cause soft shelled eggs
Anyways, sorry that was so long. Hope it helps!