You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, How can I help you?

USER: Can you please help me in changing my existing reservation?

ASSISTANT: Sure, May I know your name?

USER: I am Christopher Mitchell.

ASSISTANT: Ok, we found a reservation on your name, please provide me your travelling dates.

USER: My travel dates are from Aug 26th to Aug 28th.

ASSISTANT: Can I have your airport codes?

USER: My airport codes are from LGA to LAS.

ASSISTANT: Do you have any connection limit?

USER: I want a single connection in between my journey.

ASSISTANT: Are there any other preferences?

USER: No.

ASSISTANT: Sorry, there are no flights found with your data.

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

ASSISTANT: Thank you.