Hi John,
How are you? I wonder that @Rahul_MCAP just point the cmd-let that you need to use in order to fix this, not the exact one, with the specific parameters that you need to use. Let consider that this is the sintaxis of this cmd-let:
Convert-MsolDomainToStandard -DomainName <string> -PasswordFile <string> -SkipUserConversion <Boolean> [-Confirm] [-WhatIf] [<CommonParameters>]
As you can see, some parameters are needed.
If you need further references about this cmd-let you can take a look this article:
Convert-MsolDomainToStandard
msdn.microsoft.com/.../dn194122.aspx
Please let us know your comments,
Regards,
Oscar