Level streaming for large maps

I am an amateur game designer and I made a pretty big mistake, or maybe I didn’t. I created a large world that is all in a single level, and I am not sure how to use level streaming with this, or is there another way I can make it so parts of the world loads or renders in certain areas when certain points are reached? I got caught up in making the world I didn’t think of how to make the parts load separately.