Unfortunately, it is not possible to track the An Post shipment status if the tracking ID is lost. In case you have lost your tracking number, you can simply refer to your An Post account to find your tracking number.
In case you cannot find your An Post tracking number, you can check the confirmation email sent to you by the seller. Usually, the tracking number is part of the confirmation email sent to you after the online placing of the order.
Another way of finding your tracking ID is by logging into your An Post account by clicking on My Account and searching through the recent orders placed. There, you should be able to retrieve your lost tracking code.