Short answer: testers can send private feedback through Google Play, which you'll find in Play Console under Monitor and improve, then Ratings and reviews, then Testing feedback. Add one channel of your own, keep a simple log, and you'll have the summary Google asks for when you apply for production access.
Where Play Console puts tester feedback
Google's steps: sign in to Play Console, select your app and open the Testing feedback page. You can filter by date, language, reply state, app version or device type, and search for keywords. You can also reply to testers.
Add a second channel
Google suggests a clear feedback channel such as email, a website or a messaging forum, and even a group chat where testers can see each other's reports. A form with three fields (what you did, what you expected, what happened) gives you structured reports and space for screenshots.
Keep a feedback log
Google's tip is to maintain a record of feedback and review it regularly.…