In the bottom of a 6-quart slow cooker, add the can of cream of chicken soup, au jus gravy mix, and Beefy French onion soup mix. Pour in 1 ½ cups of water and whisk until combined.
Place cubed steaks into the gravy mixture and coated well.
Cover the slow cooker and cook on low for 6-8 hours.
30 minutes before serving, whisk together the cornstarch and cold water in a small bowl.
Remove the lid from the slow cooker and move the cubed steaks to one side, or set them aside on a plate. Pour in the cornstarch slurry and stir until it is well mixed into the gravy. Return the steaks to the sauce. Turn the setting to high and cook for 30 minutes or until the gravy is thickened.