You can go to Origins by going to the Dig Site in Excavation Site 64 in Black Ops 2.
There will be 6 generators that you need to activate. To get a generator started, simply activate the panel near the primal structure. Activating a generator will start filling a meter with zombies coming out in the area.
Most significant thing to do here is to stay close to generator until the completion bar is completely filled. There might be an incident when some zombies will start to deactivate the generator. Kill them before they succeed.
I would advise you to turn on all the generators in one round and have some decent guns at your disposal. Generators are located at different places so you will have to find them first.
Black Ops 2 Origins Zombies Generators Locations
Generator #1: In the spawn room.
Generator #2: The exit door from the first generator’s position. You will spot it in no time.
Generator #3: Take the left door from the first generator’s position. It will be on the left side.
Generator #4: Get out from the workshop to go to No Man’s Land and you will see it to your left.
Generator # 5: Come out of the workshop to No Man’s Land and see it on your right.
Generator #6: In went up church, on the far backside of the top floor.
Activating all generators will give you the access to Pack-a-Punch machine and the achievement will unlock.