The Avalon controller is listening on port 80 (http). On your router forward whatever external port you want to internal port 80 of your controllers IP.
If external port 80 is already in use pick a different one…maybe 8080 forwarded to internal port 80 of your controllers IP.
To access externally browse to
http://IP:8080 You will want to set the controller to a static IP or a DHCP reservation. For your public IP you will want to set up dynamic DNS if you don’t have a static IP from your ISP.
This will work, but is not the most secure. Does your router support VPN? I’m not going to get into how to set up a VPN, but you should look into it.