Per ABC’s official logline for the crossover episode, which was filmed in part at Dropout’s own studios in Los Angeles, “Harper and Miles feel the weight of their recent mistakes, while Harper is tasked with training Miles. Nolan and Celina are dispatched to a robbery call at the Dropout TV Studios where Nolan encounters a familiar face.”

Speculating, I'm guessing Sam is the familiar face. While filming a "normal" episode of Game Changer Sam is going to look for a prop only to discover it missing. He'll initiate a fake cut, talk with a PA, and discover it has been "stolen". The police will arrive (cast of The Rookie), and both sides the Players and The Rookie cast will attempt to solve the robbery.