You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you today?

USER: My name is Sarah Robinson. Due to sudden change in my trip I want to change my existing reservation.

ASSISTANT: Sure Sarah. I will help you with that. Please wait a minute.

USER: Ok.

ASSISTANT: Thank you for waiting. Sorry Sarah, no reservation has found under your name.

USER: It's Ok. Thank you.

ASSISTANT: Your welcome. Thank you for reaching us. Have a good day.