Select it and tap the icon (usually an upward arrow). On Mac: Use the The Unarchiver or similar utility.
You can use free tools like 7-Zip or WinRAR to join and extract these files. Install 7-Zip if you haven't already. Right-click on the first file (the one ending in .001 ). Select 7-Zip > Extract Here or Extract to [folder name] . K0KOUVCAMGCSAA9.7z.001
: Check the source where you downloaded the file to see if there are other parts you forgot to download. Select it and tap the icon (usually an upward arrow)