You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: Can you please help me to change my existing reservation?

ASSISTANT: May I know your name please?

USER: My name is Thomas Nelson.

ASSISTANT: Please wait.

USER: Sure.

ASSISTANT: I have found your reservation. Can I know your travelling dates?

USER: Sure, my travelling dates are on Feb 21 and 23.

ASSISTANT: May I know your travelling airport codes?

USER: Airport codes are SEA to DEN.

ASSISTANT: Do you have any other preference?

USER: My depart time is morning.

ASSISTANT: Sorry, no flights available on your route.

USER: Ok, thank you.

ASSISTANT: Thank you for reaching us.