Change Object list into stringlist

My issue is that I need to delete non-duplicates from a list and I tried doing this by getting a list of every item and a list of a name of one of every item and deleting every name from the list of items so all is left is are the duplicates. My issue here is the list of items are getting are not string but an Instance. How would I make it so the items im getting are strings or should I just get a different approach

Maybe add them to a table variable?