thanks, assuming i know the taxonomy ids , could it be like this ?
function my_acf_save_post_function($post_id) {
$condition = get_field('first_tax_field', $post_id, false);
// get the value checked by user
if ($condition=='36') {
update_field('second_tax_field', '78', $post_id);
}
else {
update_field('second_tax_field', '79', $post_id);
}
}