You have to download and install the F-Secure setup file from here: https://www.f-secure.com/en/web/home_global/downloads

After downloading and installing the setup file:

  • Open the app
  • Click on the profile icon in the top-right corner of the main page
  • Select "Enter subscription code"
  • Enter the product key you received after purchase and click Continue
  • Done, your product will be activated or renewed