I think we're supposed to do that every time there's a new experimental version.
Select the first and second, 'Game settings' and 'Game Data', and then hit the Clean button. You want to choose the 'Clean game data' one at the bottom.
About a 1/3 of the way down you'll see 2 tabs 'Start Game' and 'Tools'. From your Library page click the Play button for 7DTD, and select the Show Game Launcher option in the pop-up. There's also a simple way to empty the old save data using Steam.
