You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Carolyn Thomas.

ASSISTANT: What help that you are looking from our side?

USER: I am planning to change an existing reservation, due to health issue. Can you please help me out?

ASSISTANT: Sure Carolyn Thomas, I can help you with the ticket modification process.

USER: Thank you.

ASSISTANT: I have checked your ticket status and I have found your previous ticket successfully. Can you please provide the travel dates that to be changed?

USER: Sure, I would like to travel on 07/16 and return back on 07/18.

ASSISTANT: Ok, what are your preferred source and destination airport codes?

USER: My source code is CLT and destination code is BOS.

ASSISTANT: Ok, please give me a minute. I will check the availability of flights and let you know the details.

USER: Sure,take your own time.

ASSISTANT: I am really sorry for the inconvenience, I have not found any available flight based on the details you have provided.

USER: That's fine. Thank you for your information.

ASSISTANT: It's my pleasure to help you. Thank you for choosing our travel agency.