Do I need to report principal payments from my 1099-B? My 1099-B includes principal payments with the date acquired as blank but I can't continue selecting blank in 1b

No, a return of principal is not a taxable transaction and you do not need to report it. These come from nondividend distributions and reduce your basis in the stock. You may leave them off your tax return entirely as long as you still have a basis in the underlying stock.

When you sell the stock in the future, your cost basis will be reduced because of the principal payment which means your gain will be larger (or loss smaller) on the sale. 

I had a similar situation where the 1099B didn't include the cost basis but clarified it was a principal repayment.  I left the cost basis blank and then two screens later I was able to add the same cost basis as the sales price as a correction to the 1099B.