In 4D Insider, when you choose File>Open>on 4D Server... from the menu to open a database only the databases running on the default port (19813) show in the window. To connect to a database server running on another port, click the small key icon in the upper right corner of the window:
This will open an extended pane. Here you can enter the database name, IP address, and port number. Enter the IP address followed by a comma and then the port number which is being used. For example:
Then click the new button and this will create a new database option for you to open with 4D Insider.