You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I be a help for you?

USER: Sandra Hall here. I am trying to change my existing reservation, due to an emergency but it is not happening, can you help me on this?

ASSISTANT: Sure, I am here to help you. Sorry to inform you that there is no previous ticket found on your name to change the existing reservation.

USER: It's ok. Thank you for searching.

ASSISTANT: Thank you for reaching us. Have a great day.