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 help me out?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: Can you mention your name to check further?

USER: My name is Helen Roberts.

ASSISTANT: Please wait.

USER: Sure.

ASSISTANT:  Sorry, no reservation found on your given name in our database to change it.

USER: Thank you for your service.

ASSISTANT: Thank you for contacting us and have a nice day.