You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Catherine Mitchell.

ASSISTANT: Mitchell, how may I render you?

USER: Due to sudden change in my exams dates I need to change my existing reservation. Can you help me changing my reservation?

ASSISTANT: Sure, please give me a moment to check our website.

USER: Sure.

ASSISTANT: Sorry, no reservation is available by your name.

USER: No problem. Thank you for the information.

ASSISTANT: Thank you for choosing us.