How to write Iptables rules to direct OpenVPN server traffic to SSH tunnel?

Question

SSH

An OpenVPN server has been set up on an Ubuntu 20.04 server.
Open SSH tunnel to remote host

autossh -M 20000 -D 127.0.0.1:1080 -q -N  [email protected]

Actually, they are interested in rules that will not conflict with the existing ones:

-t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

-A FORWARD -i tun0 -j ACCEPT

-A FORWARD -i tun0 -o eth0 -s 10.8.0.0/24 -j ACCEPT

-A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

-A FORWARD -j REJECT

to route VPN traffic to the SSH tunnel.