As of macOS High Sierra 10.13.4, right-clicking (or ^ ctrl clicking).app packages, which are not registered with Apple by an identified developer, and choosing Open won't work, so the only option left is to enable the Anywhere option under Security and Privacy in System Preferences (at least temporarily). From:. Close System Preferences on your Mac. Open Terminal. Type the following command: sudo spctl -master-disable.
Hit enter on your keyboard. Enter your administrator password. Hit enter on your keyboard.
Allowing Third Party Applications to Install on a MacBook. Open 'System Preferences' by clicking on the Apple icon and choosing that option. Select 'Security & Privacy' from the 'System Preferences' window. Select the 'General' tab, and select the lock in the lower left corner to allow changes. Enter your computer.
This will restore the Anywhere setting and select it by default. To verify you can open System Preferences and select Security & Privacy. To return to the default and more secure GateKeeper settings, follow the same steps, changing the command to sudo spctl -master-enable.