The password of vCenter or an ESXi host is independant of the passwords you use for normal VMs.
>> I have a problem with Appliance (OS) root password ....
If you do not speak about VMs then better adjust your terminology to the language we use here.
Ulli
To reset the vCSA's root password see e.g. https://kb.vmware.com/s/article/75174 or - depending on the version/build that you are using - the links therein.
André
Can you be more explicit ? Are you facing problem to reset VC password ?
thankl you all for the support but I solved the problem rechanging the root password through the SSH access on the host.