The two ways of restarting the game are 1) Completing the game all the way through and agreeing to restart it at the end, or , 2) Manually deleting the files inside the "cache" folder.
Were you able to complete the game all the way through to restart that way? If that doesn't work, I'd suggest re-downloading the game at this point (maybe one of the files got damaged, preventing you from restarting it?).
Edit: Also, deleting the "persistent" file in the game's "saves" folder may also manually reset the game (though you may want to save the "persistent" file somewhere on your desktop just in case you need to put it back in the "saves" folder).