You have to pick one. So far as I can see, the only answer to that question is simply, you create it. You do the business. You give one mighty heave, and pops the world into 'actual' existence. As we have said, they are completely fixed, determinate.
Every detail is engraved in stone, from the beginning to the end of time.
That is simply a consequence of the fact that possible worlds exist as a matter of pure logical necessity. The actual world, actual objects, by contrast, can be 'interfered with' . An 'actual' object is an object that can be acted upon in real time. The actuality of objects depends upon the reality of time, the time of our actual world. We are not in a position to speculate where that move will take us - if indeed it is legitimate.