Sorry about the guy but ....
there's way better ways to teach a sit then pushing your pup down! You working on all of ---> Top Training Expectations for Puppies
yet? If you start marker training you won't have any trouble
I learned hand motions to make him sit, but some lady in my neighborhood gave me some advice telling me " say sit once and if he doesn't then push his butt down " but I'll be looking at the link you sent me thanks