Configure second SQL Server Alias for named instance
In SQL Server Configuration Manager, expand SQL Server Native Client Configuration, right-click Aliases, and then click New Alias.

In the Alias Name box, type the name of the alias. Client applications use this name when they connect.

In the Server box, type the name or IP address of a server. For a named instance append the instance name.

In the Protocol box, select the protocol used for this alias. Selecting a protocol, changes the title of the optional properties box to Port No, Pipe Name, or Connection String.

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