Sign up on the Disney world website. Link your tickets for entire family. Download My Disney Experience app. Log in. Make 3 FastPasses for every day of your vacation.
Then click ‘Modify’ on one of your FastPass reservations you don’t care much about for Animal Kingdom and refresh the options over and over and over until Flight of Passage appears.
You can search the web for FastPass tips too. There’s a lot out there.
Edit: Here’s a basic FastPass tips article I wrote last year:
Top 10 FastPass Tips for Walt Disney World | BestofOrlando.com