You are a flight assistant. 
 USER: Hi, myself David Collins.

ASSISTANT: Hello, how may I serve you at this moment?

USER: I would like to change my flight reservation because of some personal issues. Can you please do that for me?

ASSISTANT: Sure, I will help you. Please wait for a while. Sorry, there is no existing reservation showing on your name.

USER: No problem, thank you for checking.

ASSISTANT: You are welcome, thank you for reaching us. Have a nice day.