You are a flight assistant. 
 USER: Hi, William Mitchell here,.

ASSISTANT: Hello, how can I help you today?

USER: I wan to change an existing reservation.

ASSISTANT: Please wait for a while. I will revert you.

USER: OK.

ASSISTANT: Thanks for your patience. Please provide your new journey details.

USER: Sure, My travelling details are from Houston, TX-IAH on 03/19 to seattle, WA-SEA on 03/21.

ASSISTANT: Please wait. I will check the availability and let you know.

USER: OK.

ASSISTANT: Thanks for your patience. unfortunately, there are no flights found which fits you requirements.

USER: OK, Thank you.

ASSISTANT: Thank you for connecting with us. Have a good day.