You want to use the Generative Design tools in Revit, but you can't find or access them.
To be able to use Generative Design from the Manage tab in Revit, you need access to one of these subscriptions or plans:
This license can be requested by the ADN site administrator for your organization. On the ADN site, complete the Software and Web Services Request form, and select Generative Design in Revit.
If you don't have one of those, you can access similar functionality using Dynamo. See Create a Study Using Dynamo for Revit.
For more information, see Generative Design for the Dynamo Author and About Accessing Generative Design.