If the field groups in the parent and child theme are still the same, no edits were made in the child themes.
1) Add the load point as you originally posted to load the groups from the parent theme.
2) On the sites using the child theme delete the groups that should be loaded from the parent theme.
3) Set the private argument in the parent acf json files to true
Field groups from the parent theme will be loaded, they cannot be synced or edited in the child theme.
You cannot “rebuilt” the groups. Building new groups the fields will have new field keys and all of the data will be lost…… unless you manually edit every post, term, user where they are used.
