How to report cost basis for stock spinoff of Dow Inc

I received Cash in Lieu for a spin off of Dow Inc from Dow Dupont on April 4, 2019. Only the $ amount and date of the sale was listed on my 1099-B. no cost basis or date of acquisition. A quantity for this spinoff was given at the end of the 1099, not sure if that represents the number of shares or what.

 

According to the Dow Press release: https://www.dupont.com/news/dowdupont-completes-spin-off-of-dowinc.html

"DowDuPont common stockholders received one share of common stock of Dow for every three shares of DowDuPont common stock they held as of the close of business on March 21, 2019. DowDuPont common stockholders will also receive cash in lieu of fractional shares of Dow common stock."

 

At first I thought it was inherited stock and entered the date of death and the cost basis on that day.

How do I calclulate the cost basis, is the acquisition date April 4, and how do I go back and correct my incorrect entry as inherited stock? I have not filed yet