You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: Myself David Evans. Due to some urgent client meeting, I am going to change my existing reservation. Can you please help me in changing the reservation?

ASSISTANT: Sure, please wait a moment.

USER: Sure, I will wait for your response.

ASSISTANT: Sorry, there is no reservation found under your name.

USER: Not a big deal, anyhow thank you very much for your service.

ASSISTANT: Most welcome.