Question about how Okabe shifts from the alpha world line to the beta Hello, I'm new here so apologies if this doesn't belong.

In the anime, Okabe realizes that in order to return to the beta world line and prevent Mayuri's death he needs to reverse the actions of each D-Mail recipient. It's clear enough to me how he does this for most of the D-Mails, up until the last one.

I understand that Okabe and Daru use the IBM 5000 hack into SERN's servers and delete everyone's information, but I don't see how that affects the past. Shouldn't everything prior to that point stay intact, and only going forward events will be altered so that SERN isn't investigating them?

It's like he presses the enter key and suddenly the world line shifts past the 1% barrier as if he's sent a D-Mail, but what precisely did he send, if anything?