The TKG Extensions bundle is available for download from the same location where you download the TKG CLI.
Follow the documentation to unpack the bundle for instructions on how to install the in-cluster/shared services.
gunzip ~/Downloads/tkg-extensions-manifests-v1.2.0-vmware.1.tar-2.gz
tar -xzf ~/Downloads/tkg-extensions-manifests-v1.2.0-vmware.1.tar-2
mv tkg-extensions-v1.2.0+vmware.1 tkg-extensions
Also make sure to install the Carvel tools bundled in the TKG artifact.