You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I serve you today?

USER: Please help me in changing my existing reservation due to some problem in the dates I have booked.

ASSISTANT: Sure, we are here to help you.

USER: Thank you.

ASSISTANT: Please share me your name.

USER: I am William Gonzalez.

ASSISTANT: Please wait a minute.

USER: Ok.

ASSISTANT: Sorry, there is no active reservation found on your name to change.

USER: Ok, no issues. Thank you for giving the information.

ASSISTANT: Thank you for choosing us.