Simply shut down or re-image your bare metal machines to uninstall Tectonic.
Tectonic bare-metal clusters should be reprovisioned using the latest Tectonic bare-metal documentation. If you've setup your infrastructure as described, skip to step 4. Use the Tectonic Installer application. Then set your servers to PXE on the next boot and reboot.
ipmitool -H node.example.com -U USER -P PASS chassis bootdev pxe