You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: Due to sudden change in my trip dates I need to change my existing reservation. Can you help me changing my reservation?

ASSISTANT: Ok, I will help you with that before going to change your reservation I need your name to check it.

USER: I am John Hall.

ASSISTANT: Sorry John Hall, there is no reservation found under your name to change it.

USER: No problem, thank you for the information.

ASSISTANT: Thanks for contacting us.