Normally, when you begin the MyGM or MyLeague modes, the game will give you the option to turn “Custom Roster” on. This option appears on the same screen that allows you to adjust the difficulty, decide whether you want to do a fantasy draft, and choose whether you want to have a salary cap. Simply turn the custom roster option to On. Then, once you continue, it will take you to a screen to download a custom roster.
Solution from User MrAwesomeMatty
When you’re at the screen that lets you choose either a Normal, Expansion, or Custom league, press whatever button is designated to bring up the choice of rosters. Since I play the game on the Switch, I press the X button when these three choices are presented, and the option to choose a different roster comes up.
NBA 2K21 – All Locker / VC Codes