You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you for today?

USER: My name is Mark Walker. I have to change my ticket reservation due to some issues, can you help me?

ASSISTANT: Sure, I will help you about it.

USER: Thank you.

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

USER: Ok, that's fine, thank you for your help in finding.

ASSISTANT: My pleasure, thank you for choosing our service.