Windows 10 security will only allow you to install apps from the Microsoft store. To get around this, please follow the instructions at this link https://support.microsoft.com/en-za/help/4456067/windows-10-switch-out-of-s-mode.
If you are already out of s-mode but cannot install iTech Facilities Management, you can try the following instructions https://docs.microsoft.com/en-us/windows/application-management/sideload-apps-in-windows-10