Unfortunately, I don’t know of any way to easily fix the problem.
If the field names are unique that would make it a little easier. Even here, if the field is part of a repeater or flexible content field it’s not going to be simple. The following SQL query would do the work. You’d need to swap out the table and field names to match your after changing one of the field keys.
In the following
acf_field_name = '_'.$your_field_name
UPDATE wp_postmeta SET meta_key = "acf_field_name", meta_value = “new_field_key” WHERE meta_key = “OLD_acf_field_name” AND meta_value = “old_field_key”
