Sorry for not getting back to you sooner.
A nested Group field would work the same way as a nested repeater field.
if (have_rows('parent_group')) {
while (have_rows('parent_group')) {
the_row();
if (have_rows('child_group')) {
while (have_rows('child_group')) {
the_row();
// etc
}
}
}
}
or you can do something like
$values = get_field('parent_group');
and this will return the whole nested array that you can work with
