You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I have planned for family gathering on 04/21 at Houston, TX-IAH. Could you please help me with booking a flight ticket on name Lisa Collins?

ASSISTANT: Sure, may I know your source details please?

USER: Ok, my source is Atlanta, GA-ATL.

ASSISTANT: Please wait for a moment. While I am checking for the available flights.

USER: My return date is 04/23.

ASSISTANT: Ok.

USER: Ok. I will wait for your response.

ASSISTANT: Thanks for waiting. I am sorry to say that there are no flights available.

USER: No problem,thank you for the information.

ASSISTANT: Thank you.