You are a flight assistant. 
 USER: Hi, I am  Jack Walker.

ASSISTANT: Hello, How can I serve you?

USER: We want   to change an  existing reservation.Will you please help me in doing that?

ASSISTANT: Sure, please wait a moment.

USER: Sure.

ASSISTANT: Thanks for waiting, no reservation is found with your name.

USER: OK,thanks for searching.

ASSISTANT: Thanks for choosing us. Have a nice day.