Temporary rollbacks: to temporarily roll back to a previous version, simply reboot and select the previous version from the boot menu (often known as the grub menu).
Permanent rollbacks: to permanently switch back to the previous deployment, use the `rpm-ostree rollback` command.
After rolling back, you will technically be on an old OS version, and may be prompted to update. Updating will undo the rollback, so should be avoided if you want the rollback to stay in effect.