Place 2 frozen chicken breasts, 1 can (10.5 ounces) cream of chicken soup, 1 packet (1 ounce) dry ranch dressing mix, and 1 cup salsa into a 6-quart slow cooker.
Stir to combine the soup, ranch seasoning, and salsa around the chicken.
Cover and cook on Low for 6 to 8 hours or until the chicken is tender and shreds easily.
Remove the chicken from the slow cooker and shred it with two forks.
Return the shredded chicken to the slow cooker and stir to combine with the sauce.
Stir in ½ cup sour cream until smooth and well combined.
Add 1 prepared 16-ounce box of rotini pasta and stir until the pasta is evenly coated with the sauce.