iptables persist across reboots?

I'm a beginner at Linux for context. I added some port forwarding rules following this guide and the last step says to run "service iptables save" to make the iptables rules persist across reboots.

https://access.redhat.com/solutions/135153

Running the given command says "The service command supports only basic LSB actions (start, stop, restart, try-restart, reload, reload-or-restart, try-reload-or-restart, force-reload, status, condrestart). For other actions, please try to use systemctl."

And running systemctl says "Unknown command verb iptables."

What is the right method to table the rules persist after a reboot?