I developed W.E.L.D.E.R. in 2011 and the app was published by Ayopa Games.
In 2020, Ayopa Games decided to cease operations, and they gave me back the game to self-publish.
In many cases, developers can transfer apps between seller accounts on the App Store, to provide a seamless transition for users of the apps.
However, this is not permitted by Apple in certain cases. In this case, it's not allowed for any app that uses iCloud.
W.E.L.D.E.R. was one of the first games to use iCloud to transfer games across devices. So unfortunately, a seamless transfer was not possible.
Instead, I built a migration tool to extract all of the game data out of the legacy app, and load it into the new app. Migration includes gigawatts, game stats, leaderboard positions, achievements completed, game preferences, single player games, and the iCloud game.
Learn how to migrate your game data here.