Need to configure Automatic seamless server failover at Client side. We have configured two servers in "VTScada Thin Client/Server Setup" under Server Setup option. We have one Public IP under which we need to configure our two redundant servers.
We have created two port forwarding rules at Network router for these two servers.
Snap shot as per below,

Router we have configured as per below,

To access from Client seamless auto change over servers, what we need to do further?

Please note that we can access both server from "Anywhere URL" for both servers. Issue is we need to access one URL with Primary servers during another servers fails.

First a warning, if these servers are exposed to the public internet, even via port forwarding, you really SHOULD use HTTPS and set up server certificates as appropriate, otherwise all logon credentials are sent in clear text (base 64 encoded, but trivially decodable), see Configuring a VTScada Thin Client Server and Securing a VTScada Thin Client Server for more info.

Next, the server names in the Server Setup tab are sent to a thin client when it connects (to either server) and the client must use local (to the client) name resolution to resolve these names to IP addresses in order to make a connection. In order to "fail over", the thin client MUST resolve these two names to different IP's, otherwise they are just aliases of each other and are seen as a single server.

In addition, in general when using thin clients on the public internet, the server names on the Setup tab MUST be fully qualified domain names (FQDN), e.g. myserver.mydomain.com.