Not much we can do for this but never had it so bad guess the uneven rain causes it . My Squash ,Tomatoes and Peppers have it

Extra calcium helps, but the main cause is sporadic watering...

Yes, spread some dolomite under the plants, I added a handful for every 2 plants this year as soon as I noticed the first signs and it stopped nearly instantly. Even the affected fruit continued to develop. If it's a recurrent issue, avoid vulnerable varieties (peppers and tomatoes with blunt or concave blossom ends and short stout squash)
these started to show signs of BER but reovered with extra calcium.

So puting a few tums in the hole when you plant may have a benefit after all.

I have really bad blossom rot on some varieties and none at all on others. I've been pulling off all the bad tomatoes. This is the worst I have ever had it. Some plants haven't had even a single good tomato. I think I won't grow the varieties with the problem again.

Keith

Crushed egg shells in and around the holes solved almost all BER for my tomatoes

Some Gardner’s suggest Epsom Salt, but that is magnesium and not calcium.

A couple Generic "Tums" under each tomatoe plant.No more blossom end rot.

Main cause is uneven watering. This disrupts the calcium flow in the plant. For sure extra calcium at planting time is good. Calcium does not flow through the soil well so get it down to where the roots are.