Sir, currently Virtualizor Module for WHMCS do not support backup and up/downgrade feature. This feature is under our todo list. OS Reinstall option is available in WHMCS enduser panel.
Hostbill Module for Virtualizor is developed and supported by Hostbill team itself. You can get more information about it here :http://hostbillapp.com/features/apps/virtualizor/index.html
Please let us know if you need any further information.