Can someone explain the season 4's ending for me?

I am a bit confused. Why did Abigail destroy that universe by releasing the cleanse? She had a talk with reginald and they discussed something along the lines of correcting a mistake but I don't see how destroying the universe would fix any of it?

Then it goes into the rest of the episode where they discussed merging with the durango to cancel our the marigold and that will stop the inf time lines and looping of destroying the world?

Can anyone explain to me how that destroys them at the original timeline that prevents this from happening ever? It seemed to me it was two diff things happening

Idk I feel dumb about this season....