You have an Azure AD tenant named contoso.

net localgroup Administrators /add “AzureAD\user1@contoso.com”

This command will add the Azure AD user with the UPN of user1@contoso.com to the local Administrators group of the device1. You need to use the AzureAD prefix and double backslashes to specify the user’s domain2. You also need to enclose the user’s name in quotation marks if it contains special characters like @1.

You can run this command from an elevated command prompt on Client1, or remotely by using PowerShell or other tools1. You can also use the Intune Role Administrator role or the Additional local administrators on all Azure AD joined devices setting to manage the local administrators group on Azure AD joined devices34.