If you set the field names of the fields when setting up ACF to the name of the current custom field ACF will pick up the values the next time the post is edited.
If you want to set them all to be picked up without editing each post then that’s a bit more work. Each field in ACF has two entries in the postmeta table.
Let’s say that your field name is represented by $fieldname. The two custom fields that need to be saved are
$fieldname = your value
‘_’.$fieldname = acf field key
