Mix chicken, potatoes, salsa, broth, cumin, salt, and pepper in slow cooker. Cover and cook until chicken shreds easily with a fork and sweet potatoes are tender, about 4 hours on high or 6 hours on low.
Add beans during last 30 minutes of cooking. Shred chicken in slow cooker with 2 forks. Taste and season with salt and pepper, if needed.
Serve topped with avocado, cilantro, sour cream, and/or onion, if using.