You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. Welcome to our agency, how can I assist you today?

USER: Do you provide any change of reservation service?

ASSISTANT: Yes, we do provide the change of reservation service.

USER: Due to miscommunication with my friend, I have reserved a ticket to Houston. I would like to change my existing reservation.

ASSISTANT: Sure, I'll help you with this issue. Can you please provide on whose name you have previously reserved the ticket?

USER: I have previously reserved my ticket with the name Gregory Adams.

ASSISTANT: Hold on a moment please, let me check the data and get back to you.

USER: Sure, take your time.

ASSISTANT: Gregory Adams, there is no existing reservation found with your name in our database to change it.

USER: That' fine, may be my friend has changed it on my behalf.

ASSISTANT: Do you need any other assistance from us?

USER: No, thank you for your information.

ASSISTANT: Thank you for utilising our service, keep utilise in future too.

USER: You are welcome.