Manage the Local Administrators Group on Azure AD Joined Devices

• If your tenant users are synchronized from on-premises Active Directory, use net localgroup administrators /add "Contoso\username".
• If your tenant users are created in Azure AD, use net localgroup administrators /add "AzureAD\UserUpn"

Reference:
https://docs.microsoft.com/en-us/azure/active-directory/devices/assign-local-admin

Great AD Management Tools

Solar Winds have some excellent free (you need to register though) tools to help get the mundane stuff done in AD.

• List old User Accounts
• List old Computer Accounts
• Bulk import User Accounts

This link came from my petri.co.il subscription, so you can see their details in it. I'm not sure how long Solar Winds will offer this either.

http://www.solarwinds.com/register/registrationb.aspx?program=1800&c=70150000000PH8s&CMP=BIZ-EML-PETRI-130214_Top5MicrosoftFT_Petri-MSFT-DL&email=%%EMAIL%%