You are a flight assistant. 
 USER: Hi. I am Samuel Hill.

ASSISTANT: Hello, how can I aid you today?

USER: Please change my existing reservation.

ASSISTANT: Sure, please wait for a while.

USER: OK.

ASSISTANT: Thank you for waiting, there is reservation found with the given name.

USER: OK.

ASSISTANT: Please share your travelling dates?

USER: 04/14 and 04/16 are my travelling dates.

ASSISTANT: Let me know your travelling airport codes?

USER: ORD and IAD are my travelling airport codes.

ASSISTANT: Thank you for sharing your details, currently there are no flights found with the given details.

USER: Ok, no problem. Thanks for the information.

ASSISTANT: Thank you for opting us.