You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: Can you please change my existing reservation?

ASSISTANT: Ok, may I know your name please?

USER: Sure, please check the reservation on the name of Deborah Davis.

ASSISTANT: Ok, please allow me to check with your previous booking now.

USER: Ok, I will wait.

ASSISTANT: I am very regretful to say, there is no flight reservation available for this journey.

USER: Ok, Thank you.

ASSISTANT: Thank you for choosing us.