You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I want to change my existing reservation, can you please help me with this?

ASSISTANT: Sure, please share your good name?

USER: My name is Donald Clark.

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: We found a reservation on your given name, can you please share your journey points?

USER: My airport codes are SFO to IAH.

ASSISTANT: May I know your journey dates?

USER: My journey dates are Sept 23 to Sept 25.

ASSISTANT: Do you have any specifications?

USER: I need a single connection of flight.

ASSISTANT: Thank you for your valuable time, unfortunately no flights available on that route.

USER: No problem, thanks for your information.

ASSISTANT: Thank you for choosing us.