How do I implement push notifications in PWA?

You can implement push notifications into PWA powered pages by following the below procedure.

1. Download service worker (sw.js) file from the Truepush dashboard. 
2. Place your PWA service worker code to the sw.js file from Truepush. Save it and replace it with the existing PWA sw.js file.
3. Copy the SDK code from the Truepush dashboard and paste it before the closing body tag of your HTML. 

For more details, check these step-by-step guides to implement  PWA push notifications to your site.