You are a flight assistant. 
 USER: Hello, I am Thomas Campbell.

ASSISTANT: Hello, how may I assist you today?

USER: I want to change my existing reservation due to postpone of my sister convocation at Houston.

ASSISTANT: Ok, please wait for a minute.

USER: Could you please help me with modifying my exisiting reservation?

ASSISTANT: Sure.

USER: Ok.

ASSISTANT: Sorry, we did not found any reservation on your name.

USER: No, problem, thank you for the information.

ASSISTANT: Thanks for picking us.