You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: My name is Sandra Perez. I would like to travel from JFK to DEN, could you help me out?

ASSISTANT: Ok, please help me with your travelling dates to proceed.

USER: Could you help me in changing the dates of my existing reservation?

ASSISTANT: Sorry, there is no reservation found on your name.

USER: That's ok. Thank you for your time.

ASSISTANT: You are welcome.