When I needed to make a bland diet like this for an ill dog ... I boiled the chicken and made the rice on the stove in plain water then mixed the two. It's best to keep this diet as bland as possible whether you are feeding it for digestive or allergy purposes.
Bear in mind this is not a diet you can keep your dog for any length of time as it is lacks proper nutrition. But it is OK for a short time (no more than a week) to help with digestive problems.
If you are using this diet as an elimination diet to sort out allergies then you'll need to keep the dog on it longer and supplement with vitamins.