Did you mean to turn off the overlay for all programs/games or just some?
If you want to disable the OSD for certain programs/games and not others, you can look for the little 'E' icon in the icons on the lower right of your desktop. Click on it, and a window will pop up showing a list of programs where the overlay is disabled. You can add or remove programs from that list there to have the OSD server ignore them.
If you want to disable the OSD completely in the Precision X1 UI, you should see a button on the middle-lower right edge of the main window marked 'OSD'. Click on that to enable or disable the OSD. When disabled, you won't see the 'E' icon either.