You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Gregory Carter here.

ASSISTANT: How may I guide you today?

USER: Can you change my flight ticket reservation?

ASSISTANT: Sure, I will help you with that.

USER: Ok.

ASSISTANT: Please give me a minute.

USER: Sure.

ASSISTANT: I am sorry to say that there is no reservation found.

USER: Not a problem.

ASSISTANT: Thank you for reaching us.

USER: Thank you.