Licenses renew automatically each year. If the renewal was cancelled or failed, the reminder email links to the checkout, and app.lemonsqueezy.com/my-orders lists your orders with a renew option. No new key is needed after renewal.
Licenses bought before May 2025 through nkdev.info renew at nkdev.info/account, with the Renew Now button on the order.
See Settings → Updates.