The file is compressed in a RAR format. You must extract this file using software like WinRAR or 7-Zip to access the .nsp file inside.
Use a title manager (like Tinfoil, DBI, or SX OS installer) to install the update over the base game. POKLGEV-(RF)-UPDATE-NSWTCH-NSP-ZIPERTO.rar
Move the .nsp file to your Nintendo Switch SD card. The file is compressed in a RAR format
Extract the POKLGEV...zip file to get the .nsp update file. POKLGEV-(RF)-UPDATE-NSWTCH-NSP-ZIPERTO.rar