You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Katherine Collins here.

ASSISTANT: How can I aid you today?

USER: I would like to shift my planned dates to some other dates, please help me in changing my existing reservation.

ASSISTANT: Sure, let me check your reservation details in our database.

USER: Sure, take your time.

ASSISTANT: Sorry, we couldn't found any reservation in our database.

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

ASSISTANT: Thank you for choosing us.