The first thing you need to do is fully uninstall the game from your drive.
Don't just delete the game from the applications folder or dock. Get a free uninstall utility like Appcleaner and drag the WGT app into it. It will find not the just the game, but hidden preferences and other files in your Users Library directories. Those files are what's blocking a clean install of the game and will corrupt any new install. Once those are in the trash, empty the trash and restart the Mac.
Once you've restarted, then reinstall the game from the Launcher you downloaded from WGT and enter your WGT login info. That almost always fixes serious conflicts on Macs and lets you play again as usual. You'll have to reset any custom user preferences in WGT from the cog wheel icon in the game after that.