While I can't write this essay for you, I'm happy to give you some ideas about what you could cover in an essay.
Invictus is a film released in 2009 which follows the story of Nelson Mandela during the rugby world cup in 1995. One interesting aspect that you might wish to look into further as part of your essay is how music was used in the film. You could look into how African music and artists influenced the soundtrack and how this links with the overall theme of the film. After all, unity is one of the big themes of the film, so you could investigate if this can be also observed in the accompanying film score. Just like Mandela's aim was to unify his people, you could research if the music in the films equally represents this unity between white and Black music traditions.
Another interesting essay topic might be surrounding the theme of forgiveness. This is undoubtedly the main theme of the film and you could investigate to what extent the director has achieved to portray this theme convincingly, authentically, and successfully. You could read up about Nelson Mandela and try to find out how close to the truth the film is in its portrayal of Mandela's ability to forgive.