First, visit the official Avast website and download Avast Free Antivirus 2022. Install the antivirus software on your computer and open the program. Next, navigate to the "Subscription" or "Activation" section. Here, you will find an option to enter a license key. Enter the license key, which will extend your free license until 2038. Finally, click on the "Activate" button to apply the license and enjoy Avast Free Antivirus with a validity until 2038.