Fisher died after suffering a heart attack two years ago, shortly after filming all of her scenes for The Last Jedi.
The upcoming movie will also feature her, as the director has worked previously unused footage of Fisher as General Leia into the film.
Speaking at a panel in Pasadena, California, Abrams was explaining how he did this and when he mentioned Fisher's name, the lights on stage suddenly started flickering.
— The Brandalorian (@BrandonDavisBD)December 4, 2019
"That's amazing," the director remarked before adding, "Hi Carrie... that's so Carrie, by the way, to do that."
Abrams, who was on stage with the film's cast, also revealed how difficult it was to wrap-up the sequel Star Wars trilogy without Leia.
“And there was no way we were going to do digital Leia," he said (via InsideTheMagic). "When we went back to look at the scenes we hadn't used in The Force Awakens, what we realised was we had an opportunity."
He added: "It's still emotional and moving to think of her and how sad we all are that she's not up here sitting with us today.”
Attendees at the event included director Abrams, screenwriter Chris Terrio, Lucasfilm president Kathleen Kennedy, and actors Daisy Ridley, Oscar Isaac, John Boyega, Adam Driver, Keri Russell, Kelly Marie Tran, Naomi Ackie, Joonas Suotamo, Anthony Daniels, Richard E. Grant, and Lando himself, Billy Dee Williams.
Abrams is at the helm of the final instalment, which completes Disney's latest Star Wars trilogy after 2015's The Force Awakens and 2017's The Last Jedi.
The Rise of Skywalker is slated for release in the UK on Thursday December 19 and will be almost two-and-a-half hours long.