Once the cause of the problem was determined, God Incorporated took the usual way out of fixing the problem. It was against their charter to intervene directly so they selected a hero and gave the poor schmuck a choice of being responsible for the death of everything, or he could save the multiverses.
Enter Harry Potter, schmuck, and all around hero. Code named Fate's Bitch, aka double oh screwed. Selected to fix a problem that spanned an infinite number of universes. Was he asked? Well yes, in a way he was. God Inc told our stalwart hero that if he didn't do as he was told, GOD would be very unhappy with him and he would end up spending the remainder of his life as a sentient pimple on his Aunt Marge's buttocks.
This isn't to say that Harry entered into this agreement with God Incorporated without some hefty conditions of his own. For one thing, he had insisted that the deity that had made the original mistake be demoted and sent to Trenton, New Jersey. It was as close to hell as Harry could possibly come up with for a deity.
It should be noted that the arrival of a demigod to New Jersey went unnoticed for 78 years before she was arrested for failure to pay her income taxes. Her defiance sparked a new religious movement which nearly resulted in bankrupting the United States and did end with the second civil war.
But we digress.
Harry got carte blanche from the CEO of God Inc, the big man himself. He was allowed to do anything to fix the problem without it staining his soul. He had unlimited funds and no matter what multiverse he landed in, he had a list of contacts for everything from black market weapons to mercenaries to Bill Gate's mistresses. He could hire whole armies if he so wished as long as he corrected the error in that universe.
There were two basic requirements that Harry had to accomplish in each universe he visited.
Voldemort could not be allowed to start the second war, no matter what the cost, he had to be stopped before the muggles became aware of the magical world. The second requirement was more troublesome, he had to supervise the remaining life of one Albus Dumbledore to insure that he never threatened the multiverses again. Unfortunately that meant Harry ended up spending anywhere from 10 to 35 years in each universe since he wasn't allowed to deliberately kill the old fool. He could however set events in motion which would result in the old man's death.
God it seemed, didn't have a problem with wiping out entire planets, but he did draw the line at murder.
As a final concession Harry demanded and got the only other person who had survived the war from his original multiverse as his companion. Luna Lovegood.
God Inc. had not been happy with that particular requirement and had in fact delayed on delivering on that promise. It wasn't until he had entered multiverse number 0074530456374856110374 theta prime bip bip dash 12 wic wic nufu and proceeded to arrange for Hogwarts to be destroyed via a nuclear weapon that they gave in. Fortunately he had arranged for the attack during the summer so the loss of life was minimized, but it was at that point that God Inc realized perhaps a companion that could act as a moral compass might not be a bad idea.
Luna Lovegood as a moral compass? As far as Luna was concerned, North was an ugly color and she wouldn't point at it even if you offered her a box of fruit loops. Now south was a divine color and she frequently wore it in private since she felt it accentuated her bust line for Harry.
God Inc was less than thrilled with the results but it was too late to send her back.