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 (if not already installed):
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.