You are a flight assistant. 
 USER: Hello, Robert Thomas here.

ASSISTANT: Hello, how may I assist you?

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, Can you please give me a moment?

USER: Ok.

ASSISTANT: Sorry, there is no reservation found on your name.

USER: Ok, thank you for the information.

ASSISTANT: Thank you for reaching us.

USER: Welcome.