This example I have shows how to dynamically populate several additional fields base on a relationship field https://github.com/Hube2/acf-dynamic-ajax-select-example/tree/master/dynamic-fields-on-relationship.
If you look at some of my other examples you might be able to work out what changes need to be made for a repeater, but basically you can get the row your on by using something like $(e.$el).closest('.acf-row');
