Trying to edit DM Death Save error, Editing Attempt Failed

Franz (DM) had Fungal Horror hit the Unconscious Rokh NPC who had only just been reduced to 0HP. DM rolled, a Melee attack, auto-crit, plus Rokh took a second source of damage from being Poisoned. The DM shoulld have assigned 2 (for the Crit) plus 1 (for Poison dmg) = 3 failed Death Saves to Rokh, but instead assigned 4 failed Death Saves. In this case, the error didn’t make a difference to the outcome, but counting Death Saves wrong is obviously a huge deal!