You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Brian Gonzalez.

ASSISTANT: Brian, how can I help you today?

USER: I want to change my existing reservation. Can you please help me in this?

ASSISTANT: Sure, I will help you with that. Please wait for a moment.

USER: Sure.

ASSISTANT: Sorry Brian, there is no active reservation found under your name in our database.

USER: Not a problem, thank you.

ASSISTANT: Welcome.