Need Help For Comparing input in booking System (I'AM NOOB)

I was trying to develop a meeting room booking using laravel .Now it can add the booking detail which but i dont know how to write the validation code for checking the booked room.

I want to check the room_id ,start_at ,finish_at, from the database wheather it already booked on that spicfic room_id and time range or not if it was booked .... the system will not allow user to booked

Best regard

stonner4life