You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I help you?

USER: I am Andrew Johnson. Can you please help me in changing my existing reservation?

ASSISTANT: Sure, please wait for a while.

USER: Ok.

ASSISTANT: Sorry Johnson, there is no active reservation found with your name in our records.

USER: Ok, no problem. Thank you.

ASSISTANT: Most welcome.