You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Richard Roberts here.

ASSISTANT: How may I assist you?

USER: Unfortunately, my trip got postponed. So, I want to change my existing reservation, could you help me?

ASSISTANT: Sure, hold on for a moment.'.

USER: Sure.

ASSISTANT: Can I know the details of the flight?

USER: My travelling airport codes are OAK to LGA and the dates are 09/11 and 09/13. Make with fare 200 and limit be 1.

ASSISTANT: There are no flights matching your preferences.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you, have a good day.