Generally in a "shit just happens"/reluctant hero themed movie, the whole arch of the character is learning to take hold of their destiny. While this is a great, classic theme, it might not be what OP had in mind for their script.
Every call should have an answer in a script, action -> reaction, and that includes passive inaction, or even resistant action.
The catalyst that happens in a good movie should actually be a catalyst for something going on with your character. Independence Day: aliens just arrive and people scramble to deal with it? No.
Will is struggling not to have his ideal career ruined by his stripper girlfriend. The aliens give him both renewed life as a pilot, a chance to live his dream and the opportunity to prove himself - we know his motivations and his back story and we know the significance when he decides to take that chance, and save the world.
Jeff is struggling with the bitter end of his last relationship, and redefine the meaning of his life. The aliens solidify the meaning in his life: Living itself, and this renewed direction heals his past relationship.
Jeff's lady is struggling to save the president's career and make a name for herself apart from Jeff's past. The aliens are the catalyst to her re-prioritizing, giving Jeff a chance, and we know the significance when she welcomes Jeff back into her life.
The president is being smeared as weak and young in the papers. With the aliens comes a chance to stand tall and proud. Of course he decides to do this, leading everyone to victory.
The kids in the trailer park struggle with their disappointing father. His repeated failures and strange past with trauma make him rise the the call when the aliens arrive.
The movie is about aliens coming to earth but it's about how all the leads react and develop from those aliens, not just not dying.
If your character makes no choices, then you have no character. Sometimes that's fine. The Area 51 guy had the aliens thrust upon him, he had to deal with it or die, and he died. Will Smith's best friend from the squad had the aliens thrust upon him, and he had to deal with it or die, and he died. Adam Baldwin dealt the aliens and lived. These are side characters. That is not appropriate way to view your lead characters.
Sometimes no action is in and of itself an action as I said above, and that's fine, but you've got to be aware that's what you're writing and build from there.