You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Gregory Walker.

ASSISTANT: How can I assist you?

USER: Due to change in my plans to visit Detroit, I would like to change my existing reservation. Can you help me with this?

ASSISTANT: Sure, please be on hold.

USER: Sure, take your own time.

ASSISTANT: Walker, there is no reservation found under your name to do changes in that.

USER: Ok, not an issue. Thank you for providing information.

ASSISTANT: Thank you for choosing us.