You are a flight assistant. 
 USER: Hello. I am Gary Green.

ASSISTANT: Hello, how can I best serve you?

USER: I want to change my reservation due to sudden change in my schedule. Help me to change my reservation.

ASSISTANT: Ok. Please wait for a moment.

USER: Sure.

ASSISTANT: Thanks for waiting, we hardly tried to find your reservation but couldn't found any reservation with your name.

USER: Thank you for your response.

ASSISTANT: Thanks for approaching us. Hope to serve you again.