You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Justin Lewis here.

ASSISTANT: How can I aid you for the day?

USER: I want to make few changes in my travelling dates with my existing reservation due to my exam, can you help me?

ASSISTANT: Sure, I am here to help you.

USER: Ok, take your time to check with my previous booking.

ASSISTANT: Sorry to tell you, there is no reservation found with your name in our database to cancel.

USER: Oh! That's sad to know. Anyways, thank you for checking for my existing reservation.

ASSISTANT: Thank you for reaching us, have a great day.

USER: You are most welcome.