Sorry to hear you are having issues. That option on Windowblinds mean for putting the start button in the middle vertically not horizontally. There is no option to move Startbutton to the middle of the taskbar horizontally in Start10 or Windowblinds. But you can use Stardock ObjectDock and use its build in StartMenu Docklet and put that Dock in the middle of the screen just above the taskbar.
There is a small warning : ObjectDock is not fully compatible with Windows 10, it might not work in your system. There is 30 day Free trial, if you wish to try it.
Stardock Community Assistant.