You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Sandra Martinez.

ASSISTANT: How can I assist you today?

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

ASSISTANT: Sure, will you please give me a moment? Thanks for waiting, there is no reservation found under your name.

USER: Sure. Ok, no problem. Thank you for your information.

ASSISTANT: Thanks for reaching us, have a great day.