how to know which earbud case goes with which earbuds after they got mixed up

my 4 sets of airbuds got mixed up and are likely no longer in the cases they began with, all are no l longer working despite following Support entries on re-pairing them up using Bluetooth and also turning bluetooth on and off and pushing buttons on backs of cases. What should I do? How to tell which airbuds below to which charging cases? All are charged.