You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how best I can help you today?

USER: Due to my health problem I want to change my reservation, can you please help me to change my recent reservation?

ASSISTANT: Sure, I am gleeful to help you.

USER: Thank you.

ASSISTANT: May I know your name to trace your details?

USER: I am Jack Lee.

ASSISTANT: Thanks for providing your name, please wait.

USER: OK.

ASSISTANT: Thanks for your patience, we are glad to inform you that we found a reservation on your name. Can you please share your new journey dates?

USER: I want to fly in the flight on Apr 05 and Apr 07.

ASSISTANT: Ok, help me with your airport codes.

USER: I want to travel from OAK to DEN.

ASSISTANT: Is there any other concerns to say?

USER: I want to return in morning time.

ASSISTANT: As per your information, we found a connecting flight in Delta Airlines with a fare of 100 and the return timing is 11:00 AM. Are you okay with this?

USER: Proceed to booking.

ASSISTANT: Ok, I have changed your reservation successfully.

USER: Thank you for your help.

ASSISTANT: Thank you for availing us.