Spltoon3-(usa)-nswtch-nsp-update121-ziperto.rar -

The most stable method is using via USB (MTP Responder): Connect your Switch to your PC via USB. Launch DBI on your Switch. Select Run MTP Responder . On your PC, open the "Switch" drive in File Explorer.

The file SPLTOON3-(USA)-NSwTcH-NSP-Update121-Ziperto.rar is a compressed archive. SPLTOON3-(USA)-NSwTcH-NSP-Update121-Ziperto.rar

the extracted .nsp update file into that folder. The most stable method is using via USB

Navigate to (or "NAND Install" if you prefer). SPLTOON3-(USA)-NSwTcH-NSP-Update121-Ziperto.rar