Configure a server object in NetScaler under Load Balancing. Pick its IP address from the subnet in which the ICG is located.
Create a Load Balancing Service Group with SSL_Bridge as the Protocol. In the screenshot it is named ICG-SSLBridge Service.
Add a Service Group Member with the ICG's IP address and TCP port.
Create a Load balancing Virtual Server. The IP address and TCP port you configure here will be accessible from the Internet.
Add a Binding to the load balancing server group, binding the ICG-SSLBridge Service you created in step 2. The load balancing virtual server should now be in the state UP, and communication from the Internet should be forwarded to ICG.