By looking at pictures attached, they are not cavities but are stains. Stains can deposit due to many reasons like wrong brushing technique
Next Steps
(-) Visit a dentist or video consult
(-) You need a proper cleaning n polishing of teeth
(-) Brush twice a day in circular motion
(-) Drink a lot of water
Health Tips
It's always better to visit doctor for proper guidance n treatment plan.
Stay safe n healthy