Rogue One is the prequel you're looking for.

Rating: 10/10 (11 July 2017)

Rogue One is not only one of my favorite Star Wars films, but also one of my favorite films of all time. The great story, characters, visuals, and so forth made this film incredibly memorable, as this movie will hold a special place in my heart. Although the score sucked, and the pacing was a little choppy in the beginning, I can forgive most of that. In the end, I decided to give Rogue One "Straight V's" on theVade Review Bar or a 10 out of 10. So yes, Rogue One is the prequel you're looking for.
Read more at theVade.