Donnie darko question (spoilers)?

how does donnie create the primary universe?? people keep saying that when the engine goes into the wormhole to october 2nd at the end of the movie it's reset to the primary universe. but what i don't understand is, how does donnie CREATE the primary universe. like, how did he make it change to the primary universe? cause it seems like he didn't do anything, he just made the plane go into the wormhole. can someone help me?