Hi @blakespot
You can use the acf/load_field hook to do that, but you need to save the post and the first repeater field first before it showing up on the second repeater field. This page should give you more idea about it: https://www.advancedcustomfields.com/resources/dynamically-populate-a-select-fields-choices/.
If you don’t want to save the post first, you need to use advanced Javascript code to achieve it. This page should give you more idea about it: https://www.advancedcustomfields.com/resources/adding-custom-javascript-fields/. I believe you can use the acf.add_action('append', function( $el ){ action to check the new row in the second repeater and then update it with the data from the first repeater.
I hope this helps 🙂
