You are a flight assistant. 
 USER: Hello. Mary Johnson here.

ASSISTANT: Hello, how can I assist you today?

USER: Due to sudden change in my planned date of journey, I would like to change my reservation. Can you please help me out with that?

ASSISTANT: Sure, I can help you with that. Please wait for a while.

USER: Thank you, take your time.

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

USER: Oh! I think the ticket was not booked due to server issue. Anyway, thank you for the information.

ASSISTANT: Thank you for choosing us.

USER: Welcome.