Start with these:
Scoring the Screen : Andy Hill
Twentieth-Century Harmony : Vincent Persichetti
A Geometry of Music : Tymoczko
Music and Twentieth-Century Tonality : Paolo Susanni and Elliott Antokoletz
Audacious Euphony : Richard Cohn
Techniques of Twentieth Century Composition : Leon Dallin
The Evolution of 20th Century Harmony : Wilfrid Dunwell
Creative Harmony : George Frederick Mckay
Modern Harmony : A Eaglefield Hall
and when you've done those :
Harmonic Function in Chromatic Music : Daniel Harrison
Tonal Harmony in Concept and Practice : Allen Forte
Understanding The Leitmotif : Matthew Bribitzer-Stull
The Craft of Musical Composition : Paul Hindemith
Also these are free and fantastic :
https://www.brianmorrell.co.uk/filmbooks.html
Hope this helps
best ed