You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am John Clark.

ASSISTANT: How may I serve you at this moment?

USER:  Due to sudden change in my planned dates of journey, I would like to change my reservation. Can you please help me out with changing of my reservation?

ASSISTANT: Sure, I am here to help you.

USER: Thank you for accepting my request.

ASSISTANT: There is no existing reservation found on your name in our data base.

USER: Ok, no problem with that one. Thank you for your help.

ASSISTANT: Thank you for reaching us.