ERIC does not include names, including case names, in its subject thesaurus. So if you type in a case name as your search term it will never be presented to you as a selection option.
However ERIC does assign case names to citations as an identifier, i.e., an additional, 'unofficial' subject heading. In order to find these identifiers, you need to search
the case name
Make sure you use "v" and not "vs"
Select the case name from the bottom of the "Subject Heading" list, and search it as a keyword.
Click on the "Display" button to view your citations.