To revert to a previous version of ESXi:
Reverting an ESXi host is only valid if the host was updated using these methods:
1) VIB installation or removal
2) Profile installation or removal
3) ESXi host update using VMware Update Manager
4) Updated from a ISO
Step:
1) In the console screen of the ESXi host, press Ctrl+Alt+F2 to see the Direct Console User Interface (DCUI) screen.
2) Press F12 to view the shutdown options for the ESXi host.
3) Press F11 to reboot.
4) When the Hypervisor progress bar starts loading, press Shift+R. You will see the warning:
Current hypervisor will permanently be replaced
with build: X.X.X-XXXXXX. Are you sure? [y/n]
5) Press Y to roll back the build.
6) Press Enter to boot