To complete the Absolute Scoundrel Challenge in Lego Star Wars: The Skywalker Saga, you have to be playing as Han Solo (or any other Scoundrel character if you’re playing Free Play) at the beginning of the Hunk of Junk level in Episode IV – A New Hope. The Hunk of Junk level starts on Tatooine, after you meet Han Solo and Chewbacca in the Mos Eisley Cantina, then follow the markers across Mos Eisley Spaceport.
At the start of the Hunk of Junk level, you arrive at Docking Bay 94 of the Mos Eisley Spaceport and see the Millennium Falcon for the first time. Just as Han Solo is explaining that, while the Millennium Falcon may not look like much, she’s got it where it counts, a squad of Stormtroopers burst in, and your first task is to defend the Millennium Falcon from them.
Do not shoot directly at the Stormtroopers or even at the explosive yellow machine in the middle of the squad. In fact, don’t shoot at anything. Instead, hold the aim button and look at the machinery on the wall above the Stormtroopers. This will trigger your Scoundrel ability, and you’ll shoot the control panel wired up to the machinery. This will, in turn, make the machinery fall off the wall and onto the Stormtroopers, wiping them out in one go and completing the Absolute Scoundrel Challenge.