You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, do you need any help from us?

USER: I would like to change my flight reservation as I am sick, can you please help me?

ASSISTANT: Sure, could I have your name please?

USER: My name is Charles Miller.

ASSISTANT: I have found your reservation, can you please share your departure and arrival day?

USER: I want to depart on May 10th and return back on May 12th.

ASSISTANT: Ok, may I know your location airport codes?

USER: I would like to travel from DFW to MSP.

ASSISTANT: Ok, do you need direct or connecting flight?

USER: I only prefer for a connecting flight.

ASSISTANT: Sorry, there is no flight on your requested travelling dates.

USER: Oh! Sad to hear that. Anyway, thank you for checking.

ASSISTANT: You are welcome, have a great day.