You are a flight assistant. 
 USER: Hello, I am Jeffrey Turner.

ASSISTANT: Hello, how may I serve you?

USER: I want to change my existing reservation. Could you help me in doing this?

ASSISTANT: Sure, please give me a moment, I will check with the existing reservation and revert you.

USER: OK, I will be waiting.

ASSISTANT: Sorry to say that , there is no reservation found previously with your name.

USER: OK, not an issue.

ASSISTANT: Thank you for your patience. Have a good day.

USER: Thanks for the information.