I have two different Soviet manual translations that say the guns, on issue to a unit, were zeroed at 100 meters by the best shooters in that unit before being issued to individual soldiers. Specific parameters are laid out in how to zero, and what a correct zero was.
The manuals also contain specific instructions for both volley fire and individual marksmanship, along with how to adjust aim for altitude, colder temps, and distance.
In volley fire, an officer or senior would estimate distance, tell the squad or unit what to set their sights on, when to fire, how much to fire, and when to cease fire.
On his own, the individual was apparently expected to provide accurate aimed fire with a known zero on his rifle. The manual is quite thorough in covering aimed fire and adjusting the rear for elevation in doing so.
Denis