You need to submit an app (publish a new app or republish an existing one) on Google Play Store. You don’t know what to do with the PEPK (Play Encrypt Private Key) .jar file that is shown on the screenshot below:
You do not need to use (e.g. download or run) PEPK.jar file when submitting an app on Google Play Store. Please follow the steps described in Google Play Store Requires New AAB Format For BiznessApps App Submissions to perform the operation.