You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, How can I render you today?

USER: I am Christopher Hernandez.

ASSISTANT: Ok.

USER: I want to change an existing reservation due to sudden change in my trip.

ASSISTANT: Ok.

USER: Can you help me?

ASSISTANT: Sure, I will help you out.

USER: Ok.

ASSISTANT: Please wait for a while. I will revert to you.

USER: Ok.

ASSISTANT: Thanks for your time, but no reservation was done previously to proceed further.

USER: No issue. Thank you.

ASSISTANT: Thank you for choosing us, Have a nice day.