First you need to get two public ip's pointed toward your machine, not going to post instructions on how to do that as it greatly depends on how your setup. How 2 ip's should look, again it greatly depends on your setup.
$ ifconfig
eth0 Link encap:Ethernet HWaddr 0c:c4:7a:c3:42:9c
inet addr:149.202.207.93 Bcast:149.202.207.255 Mask:255.255.255.0
blah blah blah
eth0:0 Link encap:Ethernet HWaddr 0c:c4:7a:c3:42:9c
inet addr:54.36.135.112 Bcast:54.36.135.112 Mask:255.255.255.255
After that, point another A/AAAA record to your new ip, can be node2.example.com or a completely different domain, up to you. Get a new TLS cert for it as well.
Now here's the easy part, make a folder called .zen2 in your home directory.
$ mkdir ~/.zen2
$ nano ~/.zen2/zen.conf
now what you put in the conf is important, change the rpc port from what you had in your first node, change the TLS cert to your new one, and add two extra lines to it
onlynet=ipv4
bind= Y O U R S E C O N D I P H E R E
put your second ip there, do the same with the first node's config file but add your first ip.
Start your second node with zend -datadir=/home/user/.zen2
After that, clone the secure node tracker again with a different name and run through the setup for the second node
$ git clone https://github.com/ZencashOfficial/secnodetracker secnodetracker2
$ cd secnodetracker2
$ node setup.js
And you're done :)
You can access your other node with ./zen-cli -rpcport=SECONDNODESPORTHERE getinfo