Open server console and login as root user, or open SSH and login as an existing user with root privileges

Update your package lists and install curl:
apt update
apt install curl -y

Download and run the official Webmin repository setup script:
curl -o setup-repos.sh https://raw.githubusercontent.com/webmin/webmin/master/setup-repos.sh
sh setup-repos.sh

Install Webmin along with recommended dependencies:
apt install --install-recommends webmin -y

Enable and start the Webmin service:
systemctl enable --now webmin

If you have a firewall enabled, open the Webmin port:
ufw allow 10000/tcp

If you have Premium OS support from us, we can configure the Firewall for you.