After seeing a screen capture of the Workout Blender, the reason that you are not seeing the Create Video button is that there is no video to create yet. If you click "New Workout", name it, and click "Save", you have created a new, empty workout. The "Create Video" button will appear when you drag at least one chapter into the workout, when there is something to "Create". Hope this clears up the confusion with respect to that.
For those who cannot see the bottom portion of the window, you can try clicking on the "maximize" button (the green button at the top left of the window on Mac, and the button to the left of the red "X" in the upper right corner of the window in Windows) to see if the whole Workout Blender fits on your screen. If it still won't fit, please let me know your screen resolution and we will talk to the developers about making the minimum size of the window even smaller if possible.