To thicken your creamy chicken stew up more, you can do a few things. If you are using white beans or potatoes, you could just mash a few of them up a bit to increase the thickness. Or you could add a bit of cornstarch. To add cornstarch, thoroughly mix cornstarch into a small amount of cool water or broth. Stir the cornstarch slurry into the stew. Turn the heat back to medium and bring the stew to a boil for a few minutes then reduce heat.