Use Google Earth to open the KMZ file
Double-click the KMZ file if Google Earth is installed and set as the default app
Open Google Earth, then use File > Open and select the KMZ file
Rename the file extension from .kmz to .zip if you want to inspect its contents
Extract the ZIP file with a file archiver such as 7-Zip, WinZip, or built-in unzip tools
Open the extracted KML file in Google Earth, Google Maps, or a compatible GIS application
Use GIS software such as QGIS or ArcGIS if you need to view or edit the file
Import the KMZ file into a mapping app that supports KMZ files on mobile devices