Navigate to https://service.ringcentral.com/
Select Users
In the search bar, type in the NetID of the off boarding user
in the search result, click the checkbox next to the user
on the top, click the Disable button to deactivate the user login
then on the same top, click the Delete button to remove the user and free up the license.
Confirm on the Ticket that the user was removed from RingCentral