Found the info below in this site.
Teaching Your Miniature Schnauzer to Stay
Put your dog in a sit or down position, then step in front of him, holding a flattened palm to his face. Look him in the eye and say “Stay” in a firm voice.
After a second of motionlessness, lean down and mark “Yes!” and treat him. Then say “Okay,” which will be the release command from “Stay.”
Eventually work up to more time in the stay, then vary the time you ask for, so that your schnauzer doesn’t learn to stay only for a set amount of time.
The crucial thing is to treat while your mini schnauzer is in the stay, not after, or he’ll think that you’re rewarding the release.