You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you?

USER: I am David Lopez. Can you please help me in booking  my flight ticket from SFO to IAH?

ASSISTANT: Sure, can you share your trip dates?

USER: My travelling dates are May 21 and May 23.

ASSISTANT: Do you have any preferences?

USER: I need my depart and return tickets at morning time.

ASSISTANT: Sorry, there is no flight on your given dates.

USER: Ok, fine thank you for checking.

ASSISTANT: Thank you for reaching us.