You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you today?

USER: I want to change my existing reservation due to postpone of my exams, can you help me with that?

ASSISTANT: Sure, please share your name.

USER: My name is Charles Wilson.

ASSISTANT: Please wait a second.

USER: Sure.

ASSISTANT: Sorry, there is no reservation found under your name.

USER: No problem, thank you for the checking.

ASSISTANT: Thank you for choosing us.