Sorry, eggshells side dressed around tomatoes will not reduce or eliminate BER. Blossom End Rot while caused by a plant's inability to move calcium into the fruit, is not caused by a lack of calcium in the soil. Most places there is plenty of calcium. There is a very long explanation of why this occurs, but in short, certain conditions make BER more probable. Most common is an uneven watering situation. Dry, followed by too wet, followed by dry in rapid succession. The other major factor is temperature swings cool followed by hot, etc. These conditions usually occur in the spring and early in the fruiting season. As conditions smooth out most of the time BER conditions go away.
All that said, if you have had a soil test done and your soil is truly calcium deficient, then calcium needs to be applied in a form more usable and in recommended amounts. Very rare. Some varieties of tomatoes are more prone to BER, but like stated it usually goes away in a short amount of time.
Egg shells are organic and will not harm anything, so if you want to put them into the soil, go right ahead, but don't expect them to help BER. BER goes away relatively quickly on its own and some people think because they added something or another to the soil that was the remedy. You could do a "go away BER dance" and in a week there would be no more BER. Was the dance the cure?