kopparhavet/module/helpers/migration-helper.js

/**
 * Perform a system migration for the entire World, applying migrations for Actors, Items, and Compendium packs
 * @return {Promise}      A Promise which resolves once the migration is completed
 */
export const migrateWorld = async function () {
    ui.notifications.info(
        `Applying System Migration for version ${game.system.data.version}. Please be patient and do not close your game or shut down your server.`,
        {permanent: true}
    );

    // Migrate to v0.0.3 from v0.0.2 and v0.0.1
    game.items.forEach((item) => {
        if(item.data.type === "spell") {
            item.update({"data.roll.label": "SPELL.ROLLTITLE"});
        }
    });

    // Set the migration as complete
    game.settings.set("kopparhavet", "worldSchemaVersion", game.system.data.version);
    ui.notifications.info(`System Migration to version ${game.system.data.version} completed!`, { permanent: true });
};