Hello.
user
Hello. How may I  help you today?
assistant
I would like to change my existing reservation. Please help me out.
user
Sure, I am happy to help you. Can I know your name?
assistant
Sure, my name is Jennifer Mitchell.
user
Yes Mitchell, your reservation is found, provide me your airport codes?
assistant
Sure, my airport codes are IAD and SFO.
user
Sure, can I know your travelling dates?
assistant
My planned dates are 07/13 and 07/15.
user
Ok, wait for a minute.
assistant
Sure.
user
Sorry to say that, no flight's available based on your travelling dates.
assistant
Ok, no problem. Thank you for your information.
user
Thank you for approaching us.
assistant