Seconding the idea about reading and looking for these points.
In my snowflake for novel 2, I have the break up of a family as the first disaster, (and it's a disaster because everything to that point was about pulling the family together), the imprisonment of the MC and her buddies as a second disaster, and the explosion of a refinery/midair collision between two rockets as the third.
But these are subject to change as the story is written and I discover more.
In Star Wars IV, Luke finding his aunt and uncle dead was his first disaster. Seeing Obi Wan die was the second (I think) and the third had to do with the death star closing on the rebel base/attacking it.
Each of those changed Luke's life in a meaningful way. He had to grow from each.