I inherited an account that had a step up basis date of 8/20/19. I received the account transfer on 5/19/20. I went through the process of transferring in each lot and was able to get the transactions transferred in on 5/19/20 with a cost basis date of 8/20/19.

I have since discovered that there were some lots that were added into the account after 8/20/19 due to dividend reinvestment that I added with a cost basis of the date of the original transaction when I think they should have been transferred with a cost basis of the transfer date (5/19/20).
Example: In inherited account: 9/4/19 - 37.187 shares of F acquired. Transferred to the new account on 5/19/20, with a cost basis date of 9/4/19.
I would like to figure out how to change the cost basis date of this transaction from 9/14/29 to 5/19/20 since it was acquired after the 8/19/20 step up basis date.
Any ideas? Thanks as always for your help.