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Hi,
There is no SingleArmManipulator in omni.isaac.core.robots (refer to the API documentation here).
You may refer to the examples here for adding a manipulator robot.
It simply defines the application Class. You need to create and run the application to see things. Follow through the Hello World and the Hello Robot tutorials to find out how to do so.
You may also refer to the source code of the Bin Filling example.