Open a command prompt as Administrator and using the command line, add the user to the administrators group. As an example, if I had a user called John Doe, the command would be "net localgroup administrators AzureAD\Ku /add" without the quotes.
runas /noprofile /user:AzureAD\most.admin@talmaconsultants.com "net localgroup administrators AzureAD\Ku /add"