In a large skillet, heat oil and cook onion for 8 minutes, then add garlic and cook for 1 minute.
In a crockpot, on low heat, add chicken, cooked onions and garlic, black beans, corn, Rotels, ranch mix, and all seasonings. Stir and add cream cheese on top.
Cover and cook for 6-8 hours. Before serving, shred chicken.