Blossom end rot is usually caused by one or more of 4 causes.
1. Calcium deficiency easily fixed by working a few tablespoons of pelletized limestone into the soil at the base of the plant
Egg shells can be tilled into the soil as a preventative measure but they take way to long to break down for it to be any use on a curative basis.
2. Too much watering.
3. Too little watering.
4. Drastically uneven watering.
Since every ones soil is different, it can be difficult to tell you how much water you need to give them. Try this. Stick your fingers in the ground a inch or so down and pinch a bit of soil. When removed if it retains its shape it probably has enough water, if it crumbles apart it is time to water.
Pick off any infected fruit and dispose of it as soon as the disease shows up.
I hope this helps