If your Switch shows a microSD card error, start by reinserting the card. Power off the console, remove the card, and insert it firmly back into the slot. Check if the card is formatted correctly—go to 'System Settings' > 'Data Management' > 'Manage MicroSD Card' and select 'Check for Errors'. If the card is unreadable, connect it to a PC using a card reader to see if it’s detected. If the PC recognizes it, back up data and reformat the card to exFAT (Switch’s preferred format). If the PC doesn’t detect it, the card may be corrupted—use data recovery software (e.g., Recuva) to retrieve files, then replace the card. Avoid using cheap, unbranded cards, as they’re more prone to errors. If the error persists with a new card, the Switch’s microSD slot may be faulty—contact Nintendo Support.