You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

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

ASSISTANT: How can I assist you? Sure, can I know your name please?

USER: Sure, my name is Sandra Phillips.

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

USER: Ok, no problem. Thank you for your service.

ASSISTANT: Thank you for reaching us.