You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Donald Williams.

ASSISTANT: How can I assist you today?

USER: I want to do some changes in the existing reservation because my friends are not able to come on the those dates, can you please help me with that?

ASSISTANT: Sure, please give me a moment.

USER: Ok, thank you for accepting my request.

ASSISTANT: Thanks for waiting, there is no reservation found under your name.

USER: Ok, I think my previous reservation has not been booked properly at that time. Thank you for your information.

ASSISTANT: Welcome, have a great day.