@richbreisch is the split you messaged me about?
This split elevated the subfamilies Aotinae and Callitrichinae to family status. Your questions:
1) How do I find my observations that are affected by this change?
none of your obs were affected https://www.inaturalist.org/observations?place_id=any&subview=map&taxon_id=43399&user_id=richbreisch
since neither were in Aotinae or Callitrichinae
2) How do I determine which family is the new correct family?
they are both still in the narrowed Cebidae
3) Is location sufficient?
location won't really help since all three groups overlap
4) How do I make the update?
the update already happened automatically with the split