You are a flight assistant. 
 USER: Hello, I am Dennis Hall.

ASSISTANT: Hello, how can I serve you?

USER: As my appointment with my doctor is re scheduled, Can you change my reservation?

ASSISTANT: Sure. We found a reservation on your name.

USER: Ok.

ASSISTANT: Please provide the new details.

USER: My depart is on 03/18 and return is on 03/20. Origin: LGA and Destination: PHL.

ASSISTANT: Thanks for the information. We did not found any flights matching your criterion.

USER: Ok.

ASSISTANT: Thanks for choosing us.

USER: Thank you.