You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello.

USER: I am Dennis Hills.

ASSISTANT: How may I amend you today?

USER: Please, change my existing reservation as my dates of travel are postponed.

ASSISTANT: Sure, please wait for a while.

USER: Sure.

ASSISTANT: Thanks for your time.

USER: Ok, no worries.

ASSISTANT: We did not find any reservation on your name to proceed with change in existing reservation.

USER: Ok, thank you for information.

ASSISTANT: Thank you for reaching us.