You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: I want to change my existing reservation. Can you please help me in that?

ASSISTANT: Sure, I will help you to change your reservation.

USER: Thank you.

ASSISTANT: Ok, may I know your name?

USER: Myself Charles Wilson.

ASSISTANT: I found your reservation, please share me your new travelling dates.

USER: My trip dates are Dec 30 to Jan 01.

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

USER: My airport codes are PHX to IAH.

ASSISTANT: Ok, do you have any connection limit?

USER: I need a connecting flight.

ASSISTANT: Ok, do you have any other specifications?

USER: I need to travel in economy class with normal cost airline.

ASSISTANT: Sorry, no flights are available on your route.

USER: Ok, no problem. Thank you.

ASSISTANT: Welcome, have a nice day.