Plug the microSD card into the slot on the bottom of the Deck — it’s on the bottom below the lower right corner of the screen. The card goes in face up. You might have to use a fingernail to get it to click into place.
In Settings > System, scroll down to System Format to format your microSD card.
Hit the
Steam button, go to
Settings > System and then scroll down to
System Settings.
Under
Format SD Card, hit
Format. Formatting will erase the card and you’ll get a warning saying as much. After a few minutes, your card will be good to go.
(Optional) To set microSD card as the default storage, go to
Settings again and scroll down to
Storage. At the top, you’ll see your
Internal Drive and the new MicroSD Card. If this is the first time you’ve used an SD card, you’ll have to move over to highlight the Internal Storage and hit
X to
Make Default and set the default storage. Then you can move over to MicroSD Card and
Make Default on that one.
Regardless of whether or not you’ve set it as default, the next time you
Install a game, you’ll get the option of saving it to the Internal Drive or the MicroSD Card.