You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I would like to change my existing reservation.

ASSISTANT: Sure. Could you please mention your name?

USER: My name is Gregory Miller.

ASSISTANT: OK, please wait for a moment.

USER: OK.

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

USER: It's OK, thank you for your response.

ASSISTANT: Thanks, for contacting us.