If you are talking about the handheld star wheel dresser most people don't know how to use them. Back off the tool rest so the two feet or protrusions on the bottom of the dresser hook on the tool rest but not touching the wheel while held horizontal. You then lift the handle until the dresser makes contact with the wheel and move it across the face of the wheel. If you freehand the dresser without hooking it you will not get a trued wheel. Re-adjust the tool rest when done. If the tool rest has been ground down by the grinding wheel and is not flat this won't work as the dresser feet must move across a flat surface.
Face shield and dust mask are a must as you don't want to breathe the dust or eat a chunk of wheel if it fails.