Nintendo Switch Manual page 85

insert the microSD card into the slot.
Make sure that the logo on the microSD card is
facing you, then insert it until you hear a click.
Turn the console off before removing the microSD
card, then push the card in until it pops up and
remove it.
If the microSD card runs out of free space
If you run out of free space on your microSD card,
you can transfer the data to a higher-capacity
microSD card using a computer.
You can also use two microSD cards at the same
time without transferring any data, but please be
aware that you won't be able to consolidate data
saved in this way onto one microSD card at a later
date.
Formatting the microSD card
Formatting the microSD card will delete all data
saved on it, including software data and
screenshots.