OK, so here’s the function that should do the trick:
function modify_events_to_use_new_field() {
$events = get_posts( array(
'post_type' => 'event',
'post_status' => 'any',
'posts_per_page' => -1
) );
foreach ( $events as $event ) {
if ( preg_match('@^(.*) - ([^-]*)$@', $event->post_title, $matches) ) {
// you'll have to modify the POST_META_KEY to the real name of your custom field
update_post_meta( $event->ID, '<POST_META_KEY>', date('Ymd', strtotime($matches[2]) ) );
}
}
}
Now you have to change the name of custom field in there and run that function.