This policy setting specifies whether Cortana is allowed on the device. If you enable or don't configure this setting, Cortana will be allowed on the device. If you disable this setting, Cortana will be turned off. When Cortana is off, users will still be able to use search to find things on the device.
Administrative Templates/
Windows Components/
Local Computer Policy -> Computer Configuration -> Administrative Templates -> Windows Components -> Search
After changing group policy options, you need to update group policy. If you do not update group policy then settings will not effect. To update it just simply type below command and also sample image is shown.
gpupdate /force
In about command we used "/force" option, this will help up to update policy options forcefully.
