Help re: true reset

Alright, so I just bought the game from Steam. Before that, I had a pirated copy of the game and I had finished the pacifist run there, then I was in the middle of the genocide run.

Before I bought from Steam, I deleted all the Undertale-related files, to be sure that I'd be starting a clean slate.

The problem is that, when I opened the game via Steam...

... it loaded from my last save from the genocide run.

I've searched for ways to reset the game and all, but I can't find anything under my Steam folder or under the AppData folder.

Send help, please.

P.S. I know I'm a horrible person, Flowey. Thanks