SPOILERS for Star Wars: The Rise of Skywalker.
J.J. Abrams has explained how he convinced Harrison Ford to return for Star Wars: The Rise of Skywalker, revealing it was actually quite easy. Longtime Star Wars fans might be surprised to learn this; Ford infamously wanted his iconic smuggler Han Solo to be killed off in Return of the Jedi as a martyr to the Rebellion, but George Lucas wouldn't have it. Thirty-two years later, though, Ford finally got his wish.
In Abrams' The Force Awakens, Han tries and fails to turn his son Ben/Kylo Ren (Adam Driver) back to the light. Instead, Kylo stabs him with his cross-guard lightsaber, cementing his turn to the Dark Side and allegiance to the First Order. It's a decision that continued to haunt Kylo throughout the second film in the sequel trilogy, 2017's The Last Jedi, and was payed off during The Rise of Skywalker in a scene where Kylo is once again confronted by his father, but as a memory only. As it turns out, Ford was all too willing to reprise his role for this exchange.
During an interview with Vanity Fair, Abrams explained how he got Ford to come back for The Rise of Skywalker: "Well, I called him and I said, ‘We want to have a scene in the film between Kylo Ren and his father, would you do it?’ And he said, ‘Okay'". Abrams half-joked that's all there was to the story before going on to talk about his meeting with Ford for the film and what the actor wanted to know before he committed to the project.
“We had a meeting and talked about what it would be. Harrison, who is one of the great people ever, and incredibly thoughtful about everything that he does, all he ever wants is to understand the utility of the character. 'What is my role?' It was about sitting with him and explaining what our intention was. We talked about it for quite a while, I sent him the pages. He got it, and of course, as you can see, he was wonderful."
Ford had a fair point about Han; the character leads the attack on Endor to take down the second Death Star's shield generator in Return of the Jedi, but he doesn't really have an arc in the film. Even Han isn't sure what to do with himself after Ben turns to the dark side, which is why he's gone back to smuggling by the time The Force Awakens picks up. Ultimately, however, he plays an important role in saving his son's soul over the course of the sequel trilogy, and his return in The Rise of Skywalker was all the more impactful and necessary for it. Han might've only been a memory in the movie (which is why his dialogue is so reminiscent of what he said to Ben in The Force Awakens), but his son making peace with what he did to his father was still important from a narrative perspective. The scene even reframes Ford's famously improvised line from The Empire Strikes Back ("I know") in an unexpectedly poignant way.
As Abrams called attention to in his interview, Ford's previous grumpy attitude towards Han Solo had less to do with his dislike for the role and more to do with him feeling like there wasn't any real point to keeping the character around post-Return of the Jedi (other than for the sake of it). Once that changed, however, he was much more willing and even eager to return for his scenes in the sequel trilogy. And in the end, The Rise of Skywalker arguably gave Han about as good a sendoff as he could've gotten otherwise.
Source: Vanity Fair