I'm not sure what your problem is. Normally, you have to select "I want a reservation only”.

Please specify the exact train: origin, destination, date, departure time.

CD = czech railways.

For nearly all trains NO mandatory REservations are needed-just board and find seat without a sign that says its reserved-and most local trains do not even have that.

The SITE of CD was out of reach (or maybe  still is?) last weeks due to hacker attacks-it could only be reached from CZ IPN-sites.