Select the icon file from this download you want to apply and click CMD+C (Copy) Navigate to the application in your applications folder. Find the .app for the corresponding app. Ex. Applications > Adobe Lightroom Classic CC > Adobe Lightroom Classic CC.app Select the .app file and hold down CMD+I In the info panel for the app, click the little icon preview in the top left corner of the panel so that it's selected (it'll show an outline) Hit CMD+V to paste the icon You might be prompted to type in your admin password. Do this. Your icon should now be changed.