You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello,. Any assistance required?

USER: I want to change my existing reservation due to exams got postponed, can you help me in changing my reservation?

ASSISTANT: May I know your name?

USER: My name is James Carter.

ASSISTANT: I regret, no reservation exists by name James Carter.

USER: Thanks for your prompt response.

ASSISTANT: Thanks. Have a great day!.