Minimal requirements: Capella. Install Capella as described here (online documentation).
Read the Configuration and Extensibility (online documentation) section.
There are two options to install the Add-On:
To check that the Add-On is correctly installed, click on Help -> About Capella -> Installation Details
Check that the Basic Requirement is installed.
As of Capella 7.0.0, Requirement has been extracted from Capella core, to a dedicated addon.
If you have a model from 6.1.0 or earlier, It is required to migrate the model with Basic Requirement installed. Old Requirement data will be migrated to Basic Requirement data, and the viewpoint will be activated.
If you want to remove any requirement data from your model, you need to install Basic Requirement and migrate your model beforehand. Then, it is necessary to uninstall Basic Requirement, and use "Model Detachment" on your aird file This will clean all data associated with Basic Requirement.
Unreferencing Basic Requirement from the Viewpoint Manager will not be enough and may lead to invalid models.