You need to first collect all the mini kits on the Shadow of Malevolence level. Info on that here. You use his cheat code (eraewe) to unlock him for the cheats menu
Once done, go to the mini kit room on the Republic Ship Resolute. From the main hub, head down the elevator on the left and go to the bottom left doorway in the next section. Use your collected gold bricks to open the doors and go through the elevator.
Find Lando's pod, open and buy him. Now land a vehicle with him as your main character, either in story mode, free play mode or in the hub.