All foot pedals that I have used can be pushed just a little bit for slow, or pushed down hard for fast. It's an art to learn how to be soft or hard. Now, on the other hand, I have one that wants to stick wide open. You should see me trying to dive under the machine and pull the button up. "laughing" It's probably about time for a new one.
Seriously, some machines have a speed setting on them. We can't possibly help you if we don't know your make and model. And, even then.....you still need to read your manual if you have it. If you don't have one, most manufacturers of machines do have websites where you can read and/or download the manual for free.