If your file is for the older title, Version 1.2.0 was a major content drop:
Updates in NSP format are typically installed using homebrew tools like Goldleaf or Tinfoil . TAIKONOTRFES-(USA)-NSwTcH-NSP-Update120-Ziperto...
Taito Milestones 4 Switch NSP/XCI [UPDATE] Download - Ziperto If your file is for the older title, Version 1