Just for readers clarification this would be Cisco Unity Connection 9.x rather than Unity.
If you have the LDAP integration performed already for your CUC server, you would import the user with a customized template which includes the Help Desk role, or you can assign an empty template for the import purpose and later on assign individualy the role to the user.
Help Desk Administrator
This role allows an administrator to reset user passwords and PINs, unlock user accounts, and view user setting pages.
To assign the role individualy to the user> user> edit> roles.