How to show a name as LASTNAME, FIRSTNAME in an index?

Hi, I've generated an index in InDesign for the first time. This is a general index in which some reference entries are names and some are other things.  I see how to get the names to show up according to the person's last name (and will now go back and edit those entries accordingly), but I do not see how to get those names to show up as "Lastname, First Name." I see nothing about this in Adobe's article on indexing. Any ideas?

Many thanks!