How did 001 end up in the upside down?

How did 001 end up in the upside down? Henry Creel = Brenner’s Assistant = 001 = Vecna Then Eleven—who in this future moment discovers that she in fact does not have the blood of her siblings on her hands—defeats Henry Creel, sending him to the Upside Down where he gets blasted by lightening and burnt to a crisp and, thus, becomes Vecna.

Henry Creel = Brenner’s Assistant = 001 = Vecna

Then Eleven—who in this future moment discovers that she in fact does not have the blood of her siblings on her hands—defeats Henry Creel, sending him to the Upside Down where he gets blasted by lightening and burnt to a crisp and, thus, becomes Vecna.