You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, How can I help you?

USER: I want to change my reservation because my trip has been postponed, can you assist me?

ASSISTANT: Sure, May I know your name?

USER: Eric Robinson.

ASSISTANT: Ok, please wait a minute.

USER: Sure.

ASSISTANT: We found a reservation on your name, please provide me your travelling dates.

USER: Ok, change my airport codes to OAK to BOS.

ASSISTANT: Can I have your travelling dates?

USER: My preferred dates are July 24th and July 26th.

ASSISTANT: Do you have nay other preferences?

USER: Make sure that my return time must be evening.

ASSISTANT: Sorry, there are no flights found with your data.

USER: No problem, thank you for searching.

ASSISTANT: Thank you.