Two options are available if Gatekeeper is not allowing you to start an application not downloaded from the App Store or identified developers:
1. Press CRTL and start the application. This should allow for a verification of the application to run.
2. If this does not work, you need to show the Anywhere option to show in Preferences, Security & Privacy, General tab, Allow apps downloaded from: section
i. This obtained using the terminal app (CMD+space to search for "Terminal" or in Utilities in Applications folder).
ii. Type sudo spctl
--master-disable in the terminal window, you will need to
authenticate with the administrator password.
iii. You can now open Preferences and Security & Privacy to check that the Anywhere option is available.
iv. Start the application under this settings.
v. Finally remove the Anywhere
option by typing sudo spctl --master-enable in the
terminal window (You should not leave the Anywhere
option available for any length of time).