Lay chicken in bottom of 1 1/2 or 2-quart slow cooker. Sprinkle taco seasoning over chicken. Stir together salsa and cheese soup in bowl and pour over chicken. Cook on LOW 6-8 hours.
Remove stoneware from slow cooker with pot holders, take chicken out and shred with fork. Put chicken back into stoneware, then stir in sour cream. (Note: Depending on the tenderness level of your chicken, you may be able to shred it by simply stirring it inside the stoneware).
This is great served over rice or used as an enchilada filling.