Not sure if you found the solution, but the button can be hidden away. It might also be called "saved".
Once you click on it, then you can access the history mode. On the left sidebar, there's some "change file" text.
Once you click on that, then you can restore a specific file to a specific point in time. I don't think you revert the whole repl though - only a specific file.
Hi! Cycles are the point system of repl.it. For example, I have about 240 cycles right now. They're earned when people upvote your posts or if one of your answers to a question (on replit ask) has been marked as the "correct" answer).