what is correct format for user name that is not part of domain

Solution 1:

Login using remote server name and its registrated user. For example, I have a server sr-si-s00 and administrator as user. So simply input of sr-si-s00\administrator or .\administrator logs me in.

Solution 2:

Do you mean a local username?

Try .\username

.\ will change the domain to the local computer name

Solution 3:

Should be computername\username, as far as I see. If you have access to a VM console, login there, run cmd, type "whoami" and it will give you the complete user name including the computer name.

Solution 4:

The specific error The name provided is not a properly formed account name usually occurs when a SAMaccountname is expected but a User Principal Name (UPN) is provided instead.

You should use either computername\username or simply username