Pour 1 1/2 cups water, 1 can French onion soup, 1 can cream of chicken soup and 1 packet packet Au Jus Gravy mix into instant pot. Whisk together well.
Place 4 cubed steaks into pot making sure to coat the pieces in the gravy.
Close lid, turn valve to "Sealing." Cook on Manual High pressure for 20 minutes. Note: It will take anywhere from 5-10 minutes to come up to pressure before cooking.
If you get a "burn" message, just give it a few minutes, it will eventually start cooking. Or, open it back up, scrape the bottom really well to make sure there are no bits sticking to the bottom. Add a bit more water to thin it out a bit then try again.
After cooking, carefully turn valve to "Venting" (this is called a "Quick Release"). Be VERY careful of the steam that will quickly come out. Allow all of the steam to fully release before unlocking lid.
Turn the Instant Pot to the sauté setting. Remove the cubed steaks. In a small bowl or measuring cup, mix together 1/4 cup water with 3 Tablespoons cornstarch (this is called a "slurry").
Pour this slurry mixture into the gravy that is already in the Instant Pot. Whisk well to combine. Continue to whisk until gravy starts to thicken. Place cubed steaks back into the pot to warm them back up. Turn off Instant Pot.
Serve cubed steak with gravy over mashed potatoes.
Video
Notes
Low sodium beef consommé or beef broth can be substituted for the French Onion Soup.