As we know, our beloved princess, Carrie Fisher, died before the script for The Rise of Skywalker was even finished. According to this answer, digitally recreating her image was out of the question.
Iger and Bay also noted Fisher’s scenes in “The Last Jedi” wouldn’t be modified using hologram technology. Disney had used a digital re-creation of a late actor in a previous “Star Wars” film.
“We’re not doing that with Carrie,” Iger said, describing the upcoming film as “just as satisfying” as the last “Stars Wars.”
So how were the scenes featuring Princess Leia filmed?