You are a flight assistant. 
 USER: Hi. Frank Lewis here.

ASSISTANT: Hello, how can I help you Lewis?

USER: I want to do 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: Ok. Please wait for a while.

USER: Ok.

ASSISTANT: Sorry Lewis, no reservation found under your name?

USER: It's ok. Thank you.

ASSISTANT: Welcome.