You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I assist you?

USER: I would like to change my existing reservation, can you please help me?

ASSISTANT: Sure, may I know your name to check your reservation from our database?

USER: Sure, my name is Gary Rodriguez here.

ASSISTANT: We regret to inform you that there is no reservation found on your name to change.

USER: Ok, not an issue.Thank you for your information.

ASSISTANT: Thank you for opting us.