You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Can you please change my existing reservation?

ASSISTANT: How can I help you today? Sure I will change your reservation. May I know your name?

USER: I have reserved my flight ticket with name Donald Clark.

ASSISTANT: Sorry Donal Clark, there is no reservation done on your name.

USER: Ok, fine. Thank you for your help.

ASSISTANT: Thank you for choosing our agency.