I feel like I'm repeating myself here, because in the other thread this is already explained. But I'll give it one more shot. Most of what I'm explaining here really has nothing to do with the Access Server program itself but is just part of the way AWS works. If you want to learn more, I suggest you go through AWS documentation.
Presumably you are using an AWS EC2 instance, and this instance has a private IP assigned to it. You can see this when you're logged in to the server and type "ifconfig". A public elastic IP is almost certainly NATted 1:1 to that private IP. Amazon does this so an IP can be 'elastic', in other words, not tied to a virtual machine (or 'instance') directly, as in not configured in the operating system itself, but something that can be moved from one machine to another via the Amazon management systems. They accomplish this using NAT port forwarding, but for all ports all at once for one public IP, to one private IP. This also means there is not really a 'private' IP address like there is in for example your home network, where a private IP in your network cannot be reached from the Internet unless you specifically open ports for it in your NAT firewall port forwarding rules. On Amazon, everything is forwarded for that one public IP to the private IP of your virtual machine instance.
Simply changing the port won't make it unavailable. All ports are forwarded. You can use security groups to block ports. Security groups are like a firewall in AWS.
You can also add a dummy network adapter to your virtual machine instance and assign a private IP from a new not-conflicting range there. Since it's a dummy adapter it is purely virtual, and can only be accessed from the localhost (the server itself) or from a connected VPN client that has been given access to that IP address. Then the web interface only works when you're connected through a VPN tunnel.
Regarding the question as to how you're going to get the Connect Client and the connection profiles now that the web interface has been made unavailable, that is your problem now. There are options. You can take the files from /usr/local/openvpn_as/etc/exe/ and use them for the installation, and switch them to advanced mode if they're not already, so that the import from > file or server options become available in the system tray menu. The connection profiles can be generated from the command line of the server or downloaded from the Client web UI once you're connected through the VPN tunnel and can access the interface that way. You can also look up the documentation for command line programs to generate profiles or to generate installers for Connect Client that come with a pre-loaded connection profile. Information for this can be found in
https://docs.openvpn.net/access-server/
