Please send a screen snapshot of the Toolbox in ANSYS Workbench. I assume you are not using the Student license.
Does it show Static Structural? If so, then you are connected to a license server. The problem may be that your license does not include Harmonic Response. You will have to ask the license owner about that.
If the Toolbox is almost empty, then you are not connected to a license server. From Windows Start Menu > All Programs > ANSYS 18.0 > ANSYS Client Licensing > Client ANSYSLIC_ADMIN Utility. In that program, click Specify the License Server Machine, then Add Server Machine Spec and enter the Machine name and the port numbers. You have to ask the license owner for this info.