Sorry to hear about this. Please try to reset app preferences and check if it's working properly. If you are still experiencing the issue, let us know the DPI settings and the screen resolution of the monitor. We're here to help.
Premiere requirements include at LEAST 800 vertical pixels to your screen. This typically happens with monitors that do not have an adequate pixel dimension.
You can try clicking on a changeable setting in the Export dialog, then hitting the Tab key multiple times, as some users have found that eventually gets them to the bottom and they can see the lower controls.