* When changing an application with "Edit Application" it makes a copy of the launcher in a hidden folder
* You can show hidden folders by pressing CTRL+H in dolphin
* Navigate to the .local/share/applications/ folder (it's in your home folder)
* Delete the org.kde.dolphin.desktop file, you can see it easily as it will have your new icon.
* Close and open dolphin again
* The icon should change back to the original