You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I aid you?

USER: I am Dennis Mitchell.

ASSISTANT: Hello Dennis.

USER: I want to alter my reservation, due to postponement of concert to be held at the place where I wanted to visit, can you please take your some time for helping me?

ASSISTANT: Sure, wait a moment to check your reservation status.

USER: Ok.

ASSISTANT: Sorry Dennis, we don't found any reservation under your name.

USER: Oh, It's ok. Thank you for your information.

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