Add repository and install the Updater
Install HTTPS transport
apt install apt-transport-https
Note: this package might already be installed
Import key
curl -fsSL https://packages.cisofy.com/keys/cisofy-software-public.key | sudo gpg --dearmor -o /etc/apt/trusted.gpg.d/cisofy-software-public.gpg
Configure the software repository
echo "deb [arch=amd64 signed-by=/etc/apt/trusted.gpg.d/cisofy-software-public.gpg] https://packages.cisofy.com/customers/LICENSE/lynis-enterprise/deb/ stable main" | sudo tee /etc/apt/sources.list.d/cisofy-lynis-enterprise.list
Important note: replace LICENSE with the actual master license key.
Update repositories
apt update
Install the Lynis Enterprise Updater
apt -y install lynis-enterprise-updater