You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you today?

USER: I would like to change my existing reservation, which is done recently. Can you please help me out?

ASSISTANT: Ok, I am here to help you with that.

USER: Thank you for considering my request. Myself Brenda Collins.

ASSISTANT: May I know your good name?

USER: Brenda Collins here.

ASSISTANT: I have found the reservation.May I know your airport codes?

USER: Sure, my new preferable airport codes are IAH and AUS.

ASSISTANT: Ok, can I know your travelling dates?

USER: My new planned travel dates are from Mar 18 to Mar 20.

ASSISTANT: Please wait for a minute.

USER: Sure, I will wait for your response.

ASSISTANT: Sorry to say that, there are no flights available based on your travelling dates.

USER: That's ok, no problem. Thank you for your service.

ASSISTANT: Thank you for approaching us.