You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you today?

USER: I am Christine Johnson. I want to change my existing reservation, can you help me with that?

ASSISTANT: Sure, please wait I will check the reservation and revert to you.

USER: Ok.

ASSISTANT: Sorry, there is no reservation found on your name.

USER: Not a problem. Thank you.

ASSISTANT: Thank you for contacting us.