You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am David Nelson.

ASSISTANT: How can I help you out?

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

ASSISTANT: Sure, we are here to help you.

USER: Thank you.

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: Thanks for waiting, we did not find any active reservation on your name in our records.

USER: Ok, not an issue. Thank you.

ASSISTANT: Thank you for reaching us.