You can absolutely use pre shredded chicken in this recipe! That's actually what this recipe calls for (3 cups of pre shredded chicken), but there are options around how you get that shredded chicken - you can throw 1.25 pounds of fresh chicken in the Instant Pot or slow cooker and then shred it yourself, purchase cooked and shredded chicken from the grocery store, or grab a rotisserie chicken and shred it.