You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I guide you for today?

USER: Can you please help me to change my existing reservation?

ASSISTANT: I am happy to help you about that, can you please provide your name?

USER: Thanks for accepting my request, My name is Donald Baker.

ASSISTANT: Sorry Donald Baker, there is no active reservation under your name to change your reservation.

USER: Ok, thanks for your assistance.

ASSISTANT: You are welcome, thank you for reaching us.