You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you today?

USER: I want to change my existing reservation details, can you please help me out?

ASSISTANT: Sure, may I know your name?

USER: Sure, my name is Sandra Miller.

ASSISTANT: Wait a minute.

USER: Ok, take your time.

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

USER: It's ok, thank you for the information.

ASSISTANT: Thank you for opting us.