Small white spots on B&W negatives are usually caused by one of three things:

• air bubbles during development from insufficient or uneven agitation; these often look round
• mineral deposits from hard water drying on the film; these can look more angular
• dust settling on the film while it dries, especially if it’s hanging near an open window, vent, or other airflow

To prevent it:

• agitate consistently during development so bubbles don’t sit on the film
• keep your processing and drying area as clean as possible
• dry film in a still-air space, not near windows, fans, AC, or heating vents
• if you don’t have a dedicated drying area, a clean closet that stays closed while the film dries is a good option

For the current negatives, if the spots are already in your scans and your scanner has no cleanup feature, you’ll likely need to retouch them manually in Photoshop or similar software. If the issue is dust or dried residue on the negative surface, careful cleaning before rescanning may help, but prevention during processing and drying is the main fix.