You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Donna Williams.

ASSISTANT: How may I assist you today?

USER: I need to change my existing reservation, can you please help me with that?

ASSISTANT: Sure, please wait for a minute.

USER: Sure.

ASSISTANT: Sorry, I could not find any reservation with your name.

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Welcome.