I was working on an assembly that someone else made and was annoyed with how it was done, tried to fix it, but it was tied to a bunch of other stuff and now it is really messed up.  All I want to do is to go back to where I was when I started today.  I made the mistake of saving some of the individual parts and now it is all kinds of broken. 

I see the history folder, but I don't know how to go back.

Help... please.