Example code to migrate from ACF label based index of choice fields to a value : label based index

functions.php

<?php

add_shortcode( 'migrate_acf_choice_data', 'migrate_acf_choice_data' );
function migrate_acf_choice_data() {
    global $wpdb;
    $meta_key_to_migrate = ''; // Set the name of the acf_field to migrate the data for

    $dry_run = true; // Set to false to enable live run
    $html = '';
    
	$sql = "SELECT post_id, meta_value FROM {$wpdb->prefix}postmeta where meta_key = '{$meta_key_to_migrate}' and meta_value != ''";
	$postmetas = $wpdb->get_results( $sql );

	foreach( $postmetas as $postmeta ) {
		
		$unserialized_data = unserialize( $postmeta->meta_value );
		$new_data = array();
		
		foreach( $unserialized_data as $key => $data ) {

			if( $data == 'INSERT LABEL_1 TO SEARCH FOR HERE' ) {
				$new_data[] = '0'; // Change to corresponding value of the update ACF choice field
			}

			if( $data == 'INSERT LABEL_2 TO SEARCH FOR HERE' ) {
				$new_data[] = '1'; // Change to corresponding value of the update ACF choice field
			}
		}

		if( !empty( $new_data ) ) {
            $new_data_serialized = serialize( $new_data );
            if( $dry_run == false ) {
                $sql_update = "UPDATE {$wpdb->prefix}postmeta SET meta_value = '{$new_data_serialized}' WHERE meta_key = '{$meta_key_to_migrate}' AND post_id = '{$postmeta->post_id}';";
			    $wpdb->query( $sql_update );
            } else {
                $html .= $sql_update;
                $html .= '<br>';
            }
		}
    }
    
    return $html;
}