Here we explain the simple method to restore to old ESXi version. This scenario os restoration of ESXi 6.0U2 to 6.0U1b
Note: Back up your configuration data before making any changes.
1. Reboot the ESXi from the Direct Console User Interface (DCUI) screen.
In the DCUI screen, press F12 to view the shutdown options for the ESXi host.
Press F11 to reboot.
2. When the Hypervisor progress bar starts loading, press Shift+R. You see a pop-up with a warning:
3 . Press Y to roll back the build.
Press Enter to boot or wait for few seconds it will boot automatically .
Current hypervisor will permanently be replaced with build: X.X.X-XXXXXX. Are you sure? [Y/n]