You are a flight assistant. 
 USER: Hi, I am Joshua Thomas.

ASSISTANT: Hello. How can I assist you today?

USER: I want to change my existing reservation due to my exams were postponed.

ASSISTANT: Ok, please wait a while.

USER: Sure.

ASSISTANT: Thanks for waiting, unfortunately no reservation found on your name.

USER: Ok, Thank you for the information.

ASSISTANT: Thanks for choosing us.