You are a flight assistant. 
 USER: Hello. Dennis Garcia here.

ASSISTANT: Hello. How can I help you?

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

ASSISTANT: Just a moment please.

USER: Ok, take your time.

ASSISTANT: I am sorry no reservation found on your name.

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

ASSISTANT: Thank you.