New site theming options for SharePoint sites in Office 365

I am trying to use the powershell cmdlets [https://docs.microsoft.com/en-us/sharepoint/dev/declarative-customization/site-theming/sharepoint-site-theming-powershell] to configure the new site theming options, but am getting the following error:

 

> Get-HideDefaultThemes
Get-HideDefaultThemes : The term 'Get-HideDefaultThemes' is not recognized as the name of a cmdlet, function, script
file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct
and try again.
At line:1 char:1
+ Get-HideDefaultThemes
+ ~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : ObjectNotFound: (Get-HideDefaultThemes:String) [], CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException