Chess960 on the Chess.com mobile apps
The steps below work for both Android and iOS:
Tap the green 'Play' button on your home screen.
Tap the More drop-down menu and select 'Custom.'
Tap 'Standard' next to 'Type,' then select 'Chess960.'
Tap Play! to start your game.
Check out this article to learn more about Chess960: What is Chess 960 or Fischer Random Chess?