Easy. With each top-up, you have the option to purchase an extra data bundle. You can get as many bundles as you like with each top-up. The extra data bundle you purchase with a top-up via the My Viking app is valid for 1 month after purchase. In other words, the same as your top-up bundles.

You can only add extra data to a regular prepaid card. It's not available for Only Data SIM cards, or subscriptions.