You will be able to customize your pet and give it a new appearance or add accessories. To do this, you must press it on the main screen and enter the section.
Once you do, you will see the "Customize" button in the upper right corner, where you can purchase different outfits and appearances for your pet.
You must use credits to buy cards that will allow you to unlock various items. Each item will need a certain amount of cards in order to be equipped.
When adding a new card, you will see which item it will be applied to and, once you obtain the necessary number to unlock the item, it will appear as available.