The first part to OPC-UA configuration can be found in the TOP Server Configuration under the Project Properties.  Click on the Project Properties then go to the OPC UA tab as shown.

You will want to make sure the Server Interface is Enabled.  Only set the Log diagnostics to Yes during troubleshooting connection issue.  The Client Sessions and Browsing sections are described in detail in the help file and control how the TOP Server behaves when OPC UA Clients attempt to connect to the TOP Server.

Right Click on the Icon  and the Administration menu will be shown.

Select OPC UA Configuration from the menu to open the OPC UA Configuration Manager window as shown below.  You must have administrative privileges on the Operating System to be able to access this part of the configuration.

Click on the Edit button to adjust the level of security you are planning to use with your UA Clients.

For detailed information see the OPC UA Configuration Manager Help file installed with the TOP Server.

The check box for Enabled must be checked to connect to the TOP Server.