In order for you to transfer your existing Live App on Google Play to Appy Pie, You need to provide us with your Apps original keystore and private key, however If your app is published to Google Play and you know longer have key with which you signed your app, you will not be able to publish any updates to your app unless you unpublish the current app and publish a new app but this would mean you will lose your existing app users, ratings & reviews of your app.