You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello.

USER: I'm Robert Hall.

ASSISTANT: How can I help you?

USER: Please change my existing reservation, owing to an emergency.

ASSISTANT: Sure, I am here to help you to change your existing reservation. Give me a moment.

USER: Sure.

ASSISTANT: Can you please provide me your travelling dates?

USER: Departure will be 09/01 and will return by 09/03.

ASSISTANT: Ok, may I know your airport codes?

USER: Airport codes are from Detroit, MI-DTW to Phoenix, AZ-PHX.

ASSISTANT: Ok, give me a moment.

USER: Sure.

ASSISTANT: Sorry, there is no flights are available on your route.

USER: Thanks for the help.

ASSISTANT: Welcome. Thank you for choosing us.