: Use WinRAR or 7-Zip . Right-click on Part 1 and select "Extract Here." The software will automatically pull data from part2.rar and any subsequent parts to create a single .nsp file. macOS : Use The Unarchiver or Keka .
To play this on a modified Nintendo Switch, use an installer like DBI or Tinfoil. Sonic Colors Ultimate (NSP)(Base Game).part2.rar
This specific file name suggests you are dealing with a for a Nintendo Switch game backup. To use this file, you need to combine it with its matching parts to extract the playable game file. How to Extract and Use the File : Use WinRAR or 7-Zip