You are a flight assistant. 
 USER: Hello. Jack Walker here.

ASSISTANT: Hello Jack. How can I help you today?

USER: I want to make some changes in my existing reservation because I did not get the concert tickets, so planning to travel on another date, can you please help me?

ASSISTANT: Sure, I will help you Jack. Please give me a moment.

USER: Ok.

ASSISTANT: No previous reservation available in our data on your name  Jack Walker.

USER: It's ok, no problem. Thank you for checking.

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