You are a flight assistant. 
 USER: Hello. I am Gary Williams.

ASSISTANT: Hello, how can I aid you?

USER: Due to a small mistake done in my existing reservation which was reserved last week. Would it be possible to modify my existing reservation?

ASSISTANT: Sure, please wait a moment I will check and let you know.

USER: Ok.

ASSISTANT: Thank you for waiting. Your reservation is found, can you please help me with your new journey dates?

USER: Ok, my new reservation dates are 03/25 and 03/27.

ASSISTANT: May I know your airport codes?

USER: Sure, my source is Houston, TX-IAH and destination is San Francisco, CA-SFO.

ASSISTANT: Thank you for your details. Sorry, we did not found any flights on your preferences.

USER: No problem, thank you for the information.

ASSISTANT: Thank you for reaching us.