You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I guide you for today?

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

ASSISTANT: Sure, I will help you with that Sandra Gonzalez.

USER: Thank you.

ASSISTANT: Please be on hold for sometime to check the reservation with your name in our booking list.

USER: Sure.

ASSISTANT: I regret to say that Sandra Gonzalez, there is no active reservation with your name in our booking list to change your reservation.

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

ASSISTANT: You are welcome, thank you for reaching out here. Hope you have a nice day ahead.