Open the terminal app and type that command in.
This assumes the app is installed in the main Applications folder, you might have to customize it based on where the app is installed on your system. If you're unsure of the proper path, right-click on the app and when the menu opens, hold down the option key and you should see a menu item appear named 'Copy "IslandPlannerMac.app" as Pathname". Paste that into the terminal window and append '/Contents/MacOS/*' to the path.