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, will you mention your name please?

USER: My name is David Lopez.

ASSISTANT: Please give me a moment.

USER: Sure.

ASSISTANT: There is no reservation found under your name.

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

ASSISTANT: Welcome, have a great day.