The GameMode class has a ChoosePlayerStart function, that you can override in its blueprint/C++ class.
I’d say, you keep an integer (“StartIndex” for instance) with the index of the PlayerStart you want to choose, in a GameInstance class.
Then, when the player goes through the door, you change the index, from 0 to 1.
In the overriden function, you get all actors of class PlayerStart, and return the one at the index you saved in the GameInstance class, and that way, you get different starts depending on where you exited another level.
If you didn’t understand anything i said or need a hand let me know.