Although I am a strong believer in the 3AS, you don't really need a 3AS in a character study, which is what you are doing: A work of fiction in which the delineation of the central character's personality is more important than the plot.
So stuff happens to them, but mostly this is to show the audience the effect this has on the character. How they think, act, make decisions, solve problems, etc.
We put this character into a situation which engages them strongly, which may not even have an antagonist or villain (man vs world story, man vs cancer, etc), but it DOES contain tension: This is the important part, people turn the pages of your story because you have got them wondering "What Happens Next". The stuff that happens does not have to escalate to some breaking point or climax; although it usually does result in some change to end the story.
That needs to happen on multiple scales, from the short term (what happens in the next few pages?) to larger scales (what happens in the next chapter? The next three? How does this story end?).
Just the ultimate scale, how does the story end, is typically not enough alone to carry the reader through to the end (but in film it often is, because it is only 90 minutes or whatever).
This is why action thrillers are so popular, nearly every minute the audience is in suspense wondering "what happens next?", except for some necessary world-building and "story setup" pages, but in the thrillers the stories are necessarily very simplistic.
Your documentary doesn't have to be as packed as a thriller with suspense; some of its tension comes from dealing with a real person and a real problem. But when you edit, you want to edit to create this kind of tension: Eventually revealing everything, but not instantly. Hold bits back.
We've gone to get a blood test for antibody X. Don't cut to "No antibody X, hooray!" We are worried about antibody X, we wonder what it means and what we do next if antibody X is found. (You are doing a little education.) Our subject has emotional responses, he can't sleep. We pursue research on some other avenue, creating another line of suspense. Then a week later -- "Hooray, no antibody X!".
Of course it depends on the room you have, but the idea is the same. There is no 3AS, but there is constant tension you must maintain, you are showing your character dealing with his life, in a highly condensed form. That tension, the series of wondering "what happens next?", is what keeps the viewer glued to your story. It must be a series of overlapping questions so it gets paid off periodically, you can't just keep reminding them again and again of the same dang question, or they will FF to the end.
Character studies in fiction are like Little Women (for each of the girls). You can try to cram Little Women into a 3AS but it doesn't really fit; stuff happens to the girls and you feel like you know them, some stuff is bigger than other stuff, but in the end they have just become adults, as people do.
Your character study will follow the 3AS naturally; you have "Leaving the Normal World" already (20% of your documentary can be his "normal world" leading up to the inciting incident that makes him leave it), the second act will be him dealing with this change; the third act will be when he has succeeded or failed, or whenever you stop filming! There will be an inciting incident for you that marks why you decided to stop filming the story; a point where you believe nothing is changing anymore, it means you have run out of tension.
Remember the 3AS is descriptive, not prescriptive. It was derived from analysis of hundreds of already good known stories; it is just the natural way we humans like our stories to be told.
The only thing you need to do (after the fact, as both Galestel and Chris Sunami advise) is wrangle your bits into the lengths (I say percentages) of the story for each act. Opening on the normal world, around 15% the first hint of trouble, around 25% definitely going to leave the normal world, then trials and errors/setbacks, then whatever incident turns out to be the deciding factor for closing the documentary and wrapping things up, about 10% from the end. That is how we like our stories told.