Hey @aztectiere! To customize your pets' descriptions, what you want to do is click the Game tab, then User tab, then Customisation. This will take you to a page that has a dropdown menu and a text box. The dropdown menu will say "Mainpage" by default, which is your profile. You can click this and select one of your pets to edit their description. Just remember that your pets have to be placed in your house in order for them to be editable.

Hope that helps!