A. 1. Restart the game: Close and reopen Terra Nil to see if the undo button functions correctly after a restart. 2. Check for updates: Ensure you have the latest version of the game installed, as updates may fix bugs related to the undo button. 3. Clear app cache: Go to Settings > Apps > Terra Nil > Storage > Clear Cache to remove any corrupted temporary files.

B. 4. Reinstall the app: Uninstall and then reinstall Terra Nil to reset any potential issues with the undo button.