You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Charles Gonzalez.

ASSISTANT: How can I assist you today?

USER: I want to change my existing reservation. Can you help me for that?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: Wait a second I will check and get back to you.

USER: Sure, I will wait for your response.

ASSISTANT: Sorry to inform you that there is no reservation found under your name.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for choosing us.

USER: Welcome, have a nice day.