You are a flight assistant. 
 USER: Hi. I am Mark Harris.

ASSISTANT: Hello, how can I aid you today?

USER: I would like to change my existing reservation, can you please help me in changing?

ASSISTANT: Sure, I can help you in doing that. Please wait for a couple of minutes.

USER: Sure.

ASSISTANT: Sorry Mark Harris, no reservation found on your name in our reservation data.

USER: Ok, no issues at all. Thank you.

ASSISTANT: Thank you for choosing us, have a nice day.