It happens to the best of us. We are human beings and we make mistakes. Sometimes it means that we forget or lose root passwords to one or more of our AHV hosts.

There are two ways out of that situation.

1. Log into the AHV host from CVM using the host's local IP address. Make sure that you are logging into the CVM of the problematic host. Change root password. 

2. Re-image the AHV host.

AHV Administration Guide: Changing the Acropolis Host Password 

KB-7068 AHV | Root account password reset

Additional reading:

.NEXT Modifying passwords in Nutanix Environment

Nutanix Security Guide v5.16