I looking to create an alias on a named instance of SQL Server.

according to BOL,

Right-click SQL Server Agent, and then click Properties.
Click the Connection tab, and in the Local host server list, click the alias to which SQL Server Agent should connect.
Select an alias that refers to the local instance of Microsoft® SQL Server™ or SQL Server Agent will not work correctly


However, my Local Host Server lists is blurred out. how do i enable this ??