You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Mark Thomas here.

ASSISTANT: How can I help you?

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

ASSISTANT: Yes, I can help you.

USER: Thank you.

ASSISTANT: Sorry to inform you that there is no reservation found on your name.

USER: Oh! I think the ticket was not booked due to server issue.

ASSISTANT: Thank you for contacting us.

USER: Anyway, thank you for the information.