You can use this plugin to make your website progressive just by installing and specifying a name for your App.
In this basic free version you can only change your app name, but in the premium version there are many options to customize, icon, colors and push notifications.
Download the zip file and install.
Go to GdcPWA settings in the main menu and set the app name.
WARNING: Installing this plugin will remove/overwrite these files, service-worker.js and manifest.json if they exist in your WordPress installation root dir as they are needed by the plugin to create the PWA, if your website does not already have and use these files you can safely ignore this message.