You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: Due to my ill health, I couldn't make my trip to Philadelphia. I would like to change  my existing reservation to some other day. Can you help me with this?

ASSISTANT: Sure, I very much glad to help you in this issue. May I know your name to check your previous reservation?

USER: My previous reservation has done with my name Raymond Allen.

ASSISTANT: Ok, please wait a moment. Let me check the reservation details in our reservation list.

USER: Sure, take your own time.

ASSISTANT: Really Sorry Allen, no reservation found on your name. I guess something went wrong in your previous reservation.

USER: Ok, not an issue. May be something went wrong during my previous reservation. Thank you for providing information.

ASSISTANT: Yes. that's the reason, I didn't your reservation in my data base. Thank you for reaching us.

USER: Welcome.