You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you today?

USER: I am planning to change an existing reservation, due to health issue. Can you please change my reservation?

ASSISTANT: Sure, may I know your name please?

USER: Sure, I am Melissa Miller.

ASSISTANT: Ok, please wait for a moment.

USER: Sure, I will wait for your reply.

ASSISTANT: Sorry, there was no reservation found with your given name.

USER: That's fine, thank you for your service.

ASSISTANT: Thank you for choosing us.