How to fix this saddle for my road bike?
I think you have a mixup somewhere.  Those bolts look wrong - given there's a clearance hole in one cylinder and a threaded hole in the other, one bolt should pass through the first and thread into the second.
    +-+   +-+
[]===========&gt;
    +-+   +-+
   slip   threaded

As yours is pictured, the two bolts would push the ends of the clamp apart, if they could both get a grip.
Look around for the missing bolt.   Those two look like water bottle cage bolts, or possibly stem bolts.  What else did you take apart that may have become mixed ?