Hi Chris,
This is part of what was confusing me also. I think the key is that we're not reporting distributions for 2020. We already did that when we filed our 2020 tax returns. If you were reporting those distributions for the first time now (not sure why?), then you'd use 8915-E. But we already reported the distribution... so that's done, and therefore we're done with 8915-E. Now we just need to pay the third of the taxes owed for the 2nd and 3rd years, and the finalized form 8915-F has a very specific place for you to do that for the distribution we took in 2020.
Tony
