Cook rice mix according to package directions., Meanwhile, in a large saucepan, heat butter over medium-high heat. Add onion, celery and carrot; cook and stir until tender, 6-8 minutes. Add garlic; cook 1 minute longer. Stir in flour until blended; gradually whisk in milk and broth. Bring to a boil, stirring constantly; cook and stir until slightly thickened, 1-2 minutes., Stir in chicken and rice mixture; heat through.