You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: Myself Gary Allen.

ASSISTANT: Ok.

USER: As my trip dates have been changed. Can you help me in changing the reservation?

ASSISTANT: Sure, I have found your previous reservation. Please tell me your new travelling details.

USER: My new reservation dates are from 12/28 to 12/30. My source and destination airport codes are PHX and OAK.

ASSISTANT: Sorry, no flights found.

USER: It's ok, I will try on other dates. Thank you for your help.

ASSISTANT: Thank you for contacting us.