Have you managed to set this on full screen mode (edit: possibly if the avastUI was in full screen), given your image is 1699X900 ?
Try F11 or F12 I can't remember which toggles on/off full screen mode f11 keeps coming to mind though (confirmed f11).
If that doesn't help, try right clicking the tab on the Taskbar and select Move, use the down arrow to see if you can click the Restore button. Or alternatively try the up arrow to see if you can get to the OK button, you could also try the Tab key to see if it gets to the OK button, as you use the tab you will see focus move down,from the special scans, the OK button is two further down, 3 is cancel don't want to go there.
EDIT: Just seen that this window doesn't have full screen or Restore buttons, so the Move down option I mentioned should allow you to reach the top of the window, now you should be able to Drag the top of the window down, reducing the size. You should be able to Drag the window to the right (click and hold the Top of the window). You should now be able to Drag the Left edge to the right reducing the over all size, hopefully this should reduce the size of the window to a manageable size.
You can hold the Ctrl button down whilst closing the settings Window (X close), this should hopefully save the window size.