You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: Due to severe health issue, I want to change my trip dates. Can you please help me in changing my existing reservation?

ASSISTANT: May I know your name?

USER: My name is Jack Lee.

ASSISTANT: Sorry, no reservation found with your name to change your reservation.

USER: That's ok, thank you for your information.

ASSISTANT: Thank you for opting us.