How to delete all of an app s data?

On my iPhone, I deleted a game and reinstalled hoping to start over. But when I downloaded it had the picture of the cloud and all the old data was still saved into the game when I opened. So I went to "Manage Storage" in iCloud and deleted it from there, deleted the app and then reinstalled. Still there.

Delete the app, then delete the cloud storage for it. If it's still keeping data, it may be using a cloud specific to the game publisher.