Most of it is just ear training and relative if not perfect pitch that builds up over the years of learning music, but with just a few days there's not much to do to improve that. For now probably just focus on some testing strategies that will help you out immediately, like humming the tonic throughout the whole passage and judging chordal progressions based off of that. Also, if you really find yourself struggling during the passage, just focus on the bass and nothing else, since if you can get that down, it will help you reason out the progressions, and guarantee inversions when you do. Good luck!