‘tower-cli’ is the legacy command line tool for Ansible Tower.
‘tower-cli host’ can associate/disassociate a group to/from a host
https://tower-cli.readthedocs.io/en/latest/api_ref/resources/host.html
But now tower-cli is no longer under active development. This tool is being phased out in favor of the new official AWX CLI.
awx is the new official command-line client for AWX and Red Hat Ansible Tower
https://docs.ansible.com/ansible-tower/latest/html/towercli/index.html
the problem is that I have nowhere found an awx option allowing, like tower-cli, to associate a host with a group.