You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

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

ASSISTANT: Sure, for that I need to know your name.

USER: I am Frank allen.

ASSISTANT: Ok, please give me some time.

USER: Ok.

ASSISTANT: Unfortunately we did not find any reservation with this name.

USER: Thank you for your service.

ASSISTANT: Thanks for choosing us, have a nice day.