You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER:  I am David Thompson want to change my reservation owing an emergence. Can you help me in changing?

ASSISTANT: Sure, please wait for a while.

USER: Ok.

ASSISTANT: Sorry, no reservation found on your given name.

USER: Ok, no issues. Thank you for your help.

ASSISTANT: Thank you for choosing us.