You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Dennis Walker here.

ASSISTANT: How shall I assist you?

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

ASSISTANT: Sure, I will try my best for your. Please give me a moment to check your previous booking.

USER: Thank you. Take your time to check.

ASSISTANT: When I have checked there is no reservation found for the name which you have given.

USER: Oh! I think the ticket was not booked properly while I am booking. Anyway, thank you for the information.

ASSISTANT: It's my pleasure to help you.

USER: Welcome.