Death's Door condition occurs when your character is knocked down to 0 hit points. The way to fix this is to have another character go over to them and use the help action, which will get them back on their feet with 1 hp.
In 5e rules, when you are down you need to make a death saving throw each round. This is a roll with a difficulty class of 10. If you fail three cumulative saves first, you die. If you make three successful saves first you get back up with 1hp.
I am not sure what this game is using for the DC, but I have yet to make a single successful death saving throw in this game. Only reason I haven't had a dead character is because of the help action and the Revivify scroll (which each character gets one of in their inventory). With a DC of 10, each roll should be a 50/50 chance.
(Larian might want to think about difficulty settings for the game. I've put the EA down for now as I'm just a wimp who wants to see the story and not spend my day banging my head against a brick wall of failed dice rolls. Also might want to check to see if the dice are properly random. I mean, I know I'm a horrible roller of dice in tabletop games but...)
Z.